I can also report some oddities with the Messages app.
I’ve noticed a weird issue with Messages since upgrading to Catalina. In my Message Viewer window, I can’t see the most recent sender in the sidebar. I can see macOS notifications as the messages come in, but the messages are not visible in the list. The only way to access the most recent sender is to compose a new message and address it to that sender.
I tried quitting Messages and relaunching, as well as signing out and back in again.