I didn't see if this had been entered in as an issue but I noticed that my Conversation HIstory is no longer showing more than the 5k message limit, but in the wrong direction!
I can see the really old messages up through to 5k messages, but new messages are of course removed.
Looks like the removing of messages may want to go in the other direction. This is happening on all of the workstations running the latest version of spark (2.6.3).