Please try re-selecting the notification sound, in global app settings -- a new ROM might have reindexed the sounds, making the existing preference no longer valid.
You could also try turning off "play sound only once", "only when new messages" and "only when there are changes", as a test -- and maybe turning on "when the app is active", too, also as a test.
This will make the app always post notifications, even when there were no new unread messages *just now*, and even when the app is "open" on the screen. Just to see what happens.