Gmail Inbox on Thunderbird is suddenly empty
I've used Thunderbird to retrieve Gmail messages for years (via pop.gmail.com), and my Inbox had thousands of messages in it. Starting yesterday, my Gmail Inbox on Thunderbird shows up as having 0 messages in it. Whereas, my Gmail Sent folder is still fine on Thunderbird, and the other e-mail account I use Thunderbird with still has its Inbox fully intact.
I am using MacOS 10.13.6. I just now updated Thunderbird to version 115.16.2 but the Gmail Inbox is still empty. It can actually still receive new messages but the old ones are gone without a trace. And on the Gmail web site, all the old messages are still there (including a bunch that I had deleted on Thunderbird).
Is there a specific file corresponding to Thunderbird's copy of my Gmail Inbox that I could try to restore using TimeMachine backups?
Failing that, is there a way to prompt Thunderbird to download every message that is currently in my online Gmail Inbox?
Thank you very much for any help you can offer.