I lost my trust.

[PeterW]

I was an advocate of Thunderbird. But now I have 6 messages in my inbox, but I only see 4. This is consistent with the labels that I have: 3 unread messages, but only 2 are highlighted with boldface.

There are no message filters I can turn off. It's not a quick filter either.

Reliability is  my first priority. I can't trust you, because hide critical information.

[PeterW]

Somewhere there is a button to restore Thunderbird defaults. That fixed my problems. Unfortunately, that button is hard to find.