Unread Mail.app message count is wrong

I've had this before and I don't know why it happens.

I have multiple accounts. I collect unread counts into a double-stacked smart mailbox. It's reporting my Gmail account has 3 unread messages, which it does not. Not sure why it's thinking this but it's just obvious it's wrong.

I've rebuilt that Inbox and all smart mailboxes on top of that, which report the unread messages. Still the same thing. Restarted the app. Same thing.

Not sure what to do now. Any insight appreciated.

BTW my email system also showing other non-incoming issues, is a Proton Mail system which shows new test messages in the online interface, but not through my Bridge to the Mail.app client. I'm not sure if this might have something to do with this. I just tested another email to my Gmail account and it's showing up. My hosted Proton Mail incoming messages do not show up. And, that new unread Gmail email is not showing up in the smart mailbox that monitors that inbox. Very strange. Seems like a client issue.

Thanks for your insight. Cheers