Output of awesome --version:

awesome v4.3-897-g66b1780d (Too long)
 • Compiled against Lua 5.3.3 (running with Lua 5.3)
 • API level: 4
 • D-Bus support: yes
 • xcb-errors support: no
 • execinfo support: yes
 • xcb-randr version: 1.6
 • LGI version: 0.9.2
 • Transparency enabled: yes
 • Custom search paths: no

How to reproduce the issue:

• Add a notifications list wibox using the example at https://elv13.github.io/widgets/naughty.list.notifications.html
• Send a notification with an explicit expiry timeout: notify-send -t 2000 first
• Send a notification without an explicit expiry timeout: notify-send second

Actual result:

The first notification disappears after 2 seconds.

The second notification never disappears.

Expected result:

When no explicit expiry timeout is set, the notification should disappear after the default timeout (5 seconds).

More info

If I add this to my rc.lua:

naughty.connect_signal('added', function(n)
    print(n:get_timeout())
end)

It shows the timeout on the notification is set to the default of 5. This suggests something is wrong with its setup. To confirm this, I made this patch:

diff --git a/lib/naughty/dbus.lua a/lib/naughty/dbus.lua
index 98b36a7f..2eea8b94 100644
--- a/lib/naughty/dbus.lua
+++ a/lib/naughty/dbus.lua
@@ -278,6 +278,8 @@ function notif_methods.Notify(sender, object_path, interface, method, parameters
         end
         if expire and expire > -1 then
             args.timeout = expire / 1000
+        else
+            args.timeout = 5
         end
 
         args.freedesktop_hints = hints

With this in place, the notifications disappear.

My guess; the timer for new notifications is being created before the default timeout is set, so it sees "no timeout" and doesn't set up. I haven't been able to follow the code well enough to confirm that, let alone fix it, but there it is.