diff --git a/src/blockfilter.cpp b/src/blockfilter.cpp
index cc15fe9e5203..421d56a58aa7 100644
--- a/src/blockfilter.cpp
+++ b/src/blockfilter.cpp
@@ -3,7 +3,6 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <mutex>
-#include <sstream>
 #include <set>
 
 #include <blockfilter.h>
@@ -13,6 +12,7 @@
 #include <script/script.h>
 #include <streams.h>
 #include <util/golombrice.h>
+#include <util/string.h>
 
 /// SerType used to serialize parameters in GCS filter encoding.
 static constexpr int GCS_SER_TYPE = SER_NETWORK;
@@ -179,19 +179,7 @@ const std::set<BlockFilterType>& AllBlockFilterTypes()
 
 const std::string& ListBlockFilterTypes()
 {
-    static std::string type_list;
-
-    static std::once_flag flag;
-    std::call_once(flag, []() {
-            std::stringstream ret;
-            bool first = true;
-            for (auto entry : g_filter_types) {
-                if (!first) ret << ", ";
-                ret << entry.second;
-                first = false;
-            }
-            type_list = ret.str();
-        });
+    static std::string type_list{Join(g_filter_types, ", ", [](const auto& entry) { return entry.second; })};
 
     return type_list;
 }
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 699cd04fbe07..245b0d9b08fb 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -248,15 +248,15 @@ BOOST_AUTO_TEST_CASE(span_write_bytes)
 BOOST_AUTO_TEST_CASE(util_Join)
 {
     // Normal version
-    BOOST_CHECK_EQUAL(Join({}, ", "), "");
-    BOOST_CHECK_EQUAL(Join({"foo"}, ", "), "foo");
-    BOOST_CHECK_EQUAL(Join({"foo", "bar"}, ", "), "foo, bar");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{}, ", "), "");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{"foo"}, ", "), "foo");
+    BOOST_CHECK_EQUAL(Join(std::vector<std::string>{"foo", "bar"}, ", "), "foo, bar");
 
     // Version with unary operator
     const auto op_upper = [](const std::string& s) { return ToUpper(s); };
-    BOOST_CHECK_EQUAL(Join<std::string>({}, ", ", op_upper), "");
-    BOOST_CHECK_EQUAL(Join<std::string>({"foo"}, ", ", op_upper), "FOO");
-    BOOST_CHECK_EQUAL(Join<std::string>({"foo", "bar"}, ", ", op_upper), "FOO, BAR");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{}, ", ", op_upper), "");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{"foo"}, ", ", op_upper), "FOO");
+    BOOST_CHECK_EQUAL(Join(std::list<std::string>{"foo", "bar"}, ", ", op_upper), "FOO, BAR");
 }
 
 BOOST_AUTO_TEST_CASE(util_ReplaceAll)
diff --git a/src/util/string.h b/src/util/string.h
index 6cfa53708bb8..ce14dc865364 100644
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -58,34 +58,30 @@ void ReplaceAll(std::string& in_out, const std::string& search, const std::strin
 }
 
 /**
- * Join a list of items
+ * Join all container items. Typically used to concatenate strings but accepts
+ * containers with elements of any type.
  *
- * @param list       The list to join
- * @param separator  The separator
- * @param unary_op   Apply this operator to each item in the list
+ * @param container The items to join
+ * @param separator The separator
+ * @param unary_op  Apply this operator to each item
  */
-template <typename T, typename BaseType, typename UnaryOp>
-auto Join(const std::vector<T>& list, const BaseType& separator, UnaryOp unary_op)
-    -> decltype(unary_op(list.at(0)))
+template <typename C, typename S, typename UnaryOp>
+auto Join(const C& container, const S& separator, UnaryOp unary_op)
 {
-    decltype(unary_op(list.at(0))) ret;
-    for (size_t i = 0; i < list.size(); ++i) {
-        if (i > 0) ret += separator;
-        ret += unary_op(list.at(i));
+    decltype(unary_op(*container.begin())) ret;
+    bool first{true};
+    for (const auto& item : container) {
+        if (!first) ret += separator;
+        ret += unary_op(item);
+        first = false;
     }
     return ret;
 }
 
-template <typename T, typename T2>
-T Join(const std::vector<T>& list, const T2& separator)
+template <typename C, typename S>
+auto Join(const C& container, const S& separator)
 {
-    return Join(list, separator, [](const T& i) { return i; });
-}
-
-// Explicit overload needed for c_str arguments, which would otherwise cause a substitution failure in the template above.
-inline std::string Join(const std::vector<std::string>& list, std::string_view separator)
-{
-    return Join<std::string>(list, separator);
+    return Join(container, separator, [](const auto& i) { return i; });
 }
 
 /**
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 358010c7ce4e..c27dac169a98 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1767,16 +1767,20 @@ bool CWallet::LoadWalletFlags(uint64_t flags)
     return true;
 }
 
-bool CWallet::AddWalletFlags(uint64_t flags)
+void CWallet::InitWalletFlags(uint64_t flags)
 {
     LOCK(cs_wallet);
+
     // We should never be writing unknown non-tolerable wallet flags
     assert(((flags & KNOWN_WALLET_FLAGS) >> 32) == (flags >> 32));
+    // This should only be used once, when creating a new wallet - so current flags are expected to be blank
+    assert(m_wallet_flags == 0);
+
     if (!WalletBatch(GetDatabase()).WriteWalletFlags(flags)) {
         throw std::runtime_error(std::string(__func__) + ": writing wallet flags failed");
     }
 
-    return LoadWalletFlags(flags);
+    if (!LoadWalletFlags(flags)) assert(false);
 }
 
 int64_t CWalletTx::GetTxTime() const
@@ -4774,7 +4778,7 @@ std::shared_ptr<CWallet> CWallet::Create(interfaces::Chain* chain, interfaces::C
     {
         walletInstance->SetMinVersion(FEATURE_LATEST);
 
-        walletInstance->AddWalletFlags(wallet_creation_flags);
+        walletInstance->InitWalletFlags(wallet_creation_flags);
 
         // Only create LegacyScriptPubKeyMan when not descriptor wallet
         if (!walletInstance->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 5a36f9d662bf..6153de589846 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -1427,8 +1427,9 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
     bool IsWalletFlagSet(uint64_t flag) const override;
 
     /** overwrite all flags by the given uint64_t
-       returns false if unknown, non-tolerable flags are present */
-    bool AddWalletFlags(uint64_t flags);
+       flags must be uninitialised (or 0)
+       only known flags may be present */
+    void InitWalletFlags(uint64_t flags);
     /** Loads the flags into the wallet. (used by LoadWallet) */
     bool LoadWalletFlags(uint64_t flags);
 
diff --git a/src/wallet/wallettool.cpp b/src/wallet/wallettool.cpp
index 96ca344c4e54..8fed8c945690 100644
--- a/src/wallet/wallettool.cpp
+++ b/src/wallet/wallettool.cpp
@@ -32,7 +32,7 @@ static void WalletCreate(CWallet* wallet_instance, uint64_t wallet_creation_flag
     } else {
         wallet_instance->SetMinVersion(FEATURE_COMPRPUBKEY);
     }
-    wallet_instance->SetWalletFlag(wallet_creation_flags);
+    wallet_instance->InitWalletFlags(wallet_creation_flags);
 
     if (!wallet_instance->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
         // TODO: use here SetupGeneration instead, such as: spk_man->SetupGeneration(false);
diff --git a/test/functional/wallet_abandonconflict.py b/test/functional/wallet_abandonconflict.py
index edb3779f8228..626a594cdeae 100755
--- a/test/functional/wallet_abandonconflict.py
+++ b/test/functional/wallet_abandonconflict.py
@@ -24,6 +24,9 @@ class AbandonConflictTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 2
         self.extra_args = [["-minrelaytxfee=0.00001"], []]
+        # whitelist peers to speed up tx relay / mempool sync
+        for args in self.extra_args:
+            args.append("-whitelist=noban@127.0.0.1")
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
diff --git a/test/functional/wallet_balance.py b/test/functional/wallet_balance.py
index 242bd76bfc17..04826233cfa7 100755
--- a/test/functional/wallet_balance.py
+++ b/test/functional/wallet_balance.py
@@ -53,6 +53,9 @@ def set_test_params(self):
             ['-limitdescendantcount=3'],  # Limit mempool descendants as a hack to have wallet txs rejected from the mempool
             [],
         ]
+        # whitelist peers to speed up tx relay / mempool sync
+        for args in self.extra_args:
+            args.append("-whitelist=noban@127.0.0.1")
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
diff --git a/test/functional/wallet_basic.py b/test/functional/wallet_basic.py
index 79eb44fa2513..8d393a6f0886 100755
--- a/test/functional/wallet_basic.py
+++ b/test/functional/wallet_basic.py
@@ -27,11 +27,11 @@ def set_test_params(self):
         self.num_nodes = 4
         if self.options.descriptors:
             self.extra_args = [[
-                "-acceptnonstdtxn=1"
+                "-acceptnonstdtxn=1", "-whitelist=noban@127.0.0.1"
             ] for i in range(self.num_nodes)]
         else:
             self.extra_args = [[
-                "-acceptnonstdtxn=1",
+                "-acceptnonstdtxn=1", "-whitelist=noban@127.0.0.1",
                 '-usehd={:d}'.format(i%2==0)
             ] for i in range(self.num_nodes)]
         self.setup_clean_chain = True
diff --git a/test/functional/wallet_encryption.py b/test/functional/wallet_encryption.py
index 126cb9c4f986..37a79640664d 100755
--- a/test/functional/wallet_encryption.py
+++ b/test/functional/wallet_encryption.py
@@ -9,8 +9,7 @@
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_raises_rpc_error,
-    assert_greater_than,
-    assert_greater_than_or_equal,
+    assert_equal,
 )
 
 
@@ -76,23 +75,18 @@ def run_test(self):
 
         self.log.info('Check a timeout less than the limit')
         MAX_VALUE = 100000000
-        expected_time = self.mocktime + MAX_VALUE - 600
+        now = int(time.time())
+        self.nodes[0].setmocktime(now)
+        expected_time = now + MAX_VALUE - 600
         self.nodes[0].walletpassphrase(passphrase2, MAX_VALUE - 600)
-        self.bump_mocktime(1)
-        # give buffer for walletpassphrase, since it iterates over all encrypted keys
-        expected_time_with_buffer = self.mocktime + MAX_VALUE - 600
         actual_time = self.nodes[0].getwalletinfo()['unlocked_until']
-        assert_greater_than_or_equal(actual_time, expected_time)
-        assert_greater_than(expected_time_with_buffer, actual_time)
+        assert_equal(actual_time, expected_time)
 
         self.log.info('Check a timeout greater than the limit')
-        expected_time = self.mocktime + MAX_VALUE - 1
+        expected_time = now + MAX_VALUE
         self.nodes[0].walletpassphrase(passphrase2, MAX_VALUE + 1000)
-        self.bump_mocktime(1)
-        expected_time_with_buffer = self.mocktime + MAX_VALUE
         actual_time = self.nodes[0].getwalletinfo()['unlocked_until']
-        assert_greater_than_or_equal(actual_time, expected_time)
-        assert_greater_than(expected_time_with_buffer, actual_time)
+        assert_equal(actual_time, expected_time)
 
 
 if __name__ == '__main__':
diff --git a/test/functional/wallet_groups.py b/test/functional/wallet_groups.py
index 3eb6a8fa3c76..4912e97cd1c3 100755
--- a/test/functional/wallet_groups.py
+++ b/test/functional/wallet_groups.py
@@ -25,6 +25,10 @@ def set_test_params(self):
             ["-maxapsfee=0.00000293"],
             ["-maxapsfee=0.00000294"],
         ]
+        # whitelist peers to speed up tx relay / mempool sync
+        for args in self.extra_args:
+            args.append("-whitelist=noban@127.0.0.1")
+
         self.rpc_timeout = 480
         self.supports_cli = False
 
diff --git a/test/functional/wallet_hd.py b/test/functional/wallet_hd.py
index 7f191aa4d3fd..586ad4a8c7cf 100755
--- a/test/functional/wallet_hd.py
+++ b/test/functional/wallet_hd.py
@@ -19,6 +19,9 @@ def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 2
         self.extra_args = [['-usehd=0'], ['-usehd=1', '-keypool=0']]
+        # whitelist peers to speed up tx relay / mempool sync
+        for args in self.extra_args:
+            args.append("-whitelist=noban@127.0.0.1")
 
     def setup_network(self):
         self.add_nodes(self.num_nodes, self.extra_args)
diff --git a/test/functional/wallet_importdescriptors.py b/test/functional/wallet_importdescriptors.py
index c3c11ee11fa7..afbfd91797a1 100755
--- a/test/functional/wallet_importdescriptors.py
+++ b/test/functional/wallet_importdescriptors.py
@@ -34,6 +34,9 @@ def set_test_params(self):
         self.extra_args = [[],
                            ["-keypool=5"]
                           ]
+        # whitelist peers to speed up tx relay / mempool sync
+        for args in self.extra_args:
+            args.append("-whitelist=noban@127.0.0.1")
         self.setup_clean_chain = True
         self.wallet_names = []
 
diff --git a/test/functional/wallet_listreceivedby.py b/test/functional/wallet_listreceivedby.py
index 040bc5e40251..33ddc104c352 100755
--- a/test/functional/wallet_listreceivedby.py
+++ b/test/functional/wallet_listreceivedby.py
@@ -17,6 +17,8 @@
 class ReceivedByTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 2
+        # whitelist peers to speed up tx relay / mempool sync
+        self.extra_args = [["-whitelist=noban@127.0.0.1"]] * self.num_nodes
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()
diff --git a/test/functional/wallet_listsinceblock.py b/test/functional/wallet_listsinceblock.py
index 969d981a777a..d8acff8abe32 100755
--- a/test/functional/wallet_listsinceblock.py
+++ b/test/functional/wallet_listsinceblock.py
@@ -22,6 +22,8 @@ class ListSinceBlockTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 4
         self.setup_clean_chain = True
+        # whitelist peers to speed up tx relay / mempool sync
+        self.extra_args = [["-whitelist=noban@127.0.0.1"]] * self.num_nodes
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()