Warn about client-side tags being dropped

content/en-us/reference/engine/classes/CollectionService.yaml

@@ -51,9 +51,15 @@ methods:
       signal created by `Class.CollectionService:GetInstanceAddedSignal()` with
       the given tag.
 
-      **Warning:** When tagging an instance, it is common that some resources
-      are used to give the tag its functionality, e.g. event connections or
-      tables. To prevent memory leaks, it is a good idea to clean these up
+      ##### Warnings
+
+      - An instance's tags that were added client-side will be dropped if the server
+      later adds or removes a tag on that instance, because the server replicates all
+      tags together and overwrites previous tags.
+
+      - When tagging an instance, it is common that some resources
+      are used to give the tag its functionality, for example event connections or
+      tables. To prevent memory leaks, it's a good idea to clean these up
       (disconnect, set to nil, etc) when no longer needed for a tag. Do this
       when calling `Class.CollectionService:RemoveTag()`, calling
       `Class.Instance:Destroy()` or in a function connected to a signal returned

content/en-us/reference/engine/classes/Instance.yaml

@@ -321,6 +321,8 @@ methods:
       already applied. Successfully adding a tag will fire a signal created by
       `Class.CollectionService:GetInstanceAddedSignal()` with the given tag.
 
+      **Warning:** An instance's tags that were added client-side will be dropped if the server later adds or removes a tag on that instance, because the server replicates all tags together and overwrites previous tags.
+
       Note that when tagging an instance, it's common that some resources are
       used to give the tag its functionality, for example event connections or
       tables. To prevent memory leaks, it's a good idea to clean these up