Sometimes accounts get unsubscribed with an update. Try this: right-click on the unified inbox, select properties and then subscribe to the desired inboxes.

That worked!

To clarify for future readers of this note, I clicked "Choose" and then checked each of the "Inbox" entries for the 5 email accts that are fetched by Thunderbird.

I only include that because there's nothing that says "Subscribe" in the box. I just guessed that's what you meant.

Thanks for the quick reply!

You're welcome. And I'm glad you understood what I meant. If you would, please mark this solved, so that it gets removed from open issues. Thankyou.