macOS Catalina - Messages app - cannot delete conversations

I find repeatedly in Messages that I'm unable to delete a conversation - the "x" does not appear when I float over the conversation -- always just the one at the top of the list. I have to either quit/relaunch the app or sometimes scroll down the conversations list and back to get the "x" to return.

Bug report filed. Noticed that El Capitan is the most recent Messages version offered in the menu - even though the OS menu is current.