TB is sending most email to wrong folder

So if you have disabled all filters, how would Thunderbird be doing this?

Thunderbird has only a couple of ways to move messages. When you delete them, when they are marked as spam and when you use a filter on them. I am assuming the "bridge" folder is not the deleted or spam folder and as you have disabled all filters I am out of defaults. So I think you need to be looking further afield.like antivirus, mail provider or even "what is going in the bridge folder"? Is it the minutes of your bridge club meetings. or is it something the proton mail bridge software creates? Often context is the most important part.

Well, I think I have found the problem. I had one set of filters for my email address and another set for Local Folders. I didn't realize that I had the second set when I disabled the first set and saw nothing in the log file.

In the second set there was an entry for sending messages to the "bridge" folder. It had a line in it to send to the bridge folder if the subject was empty. That is, there was nothing, not even a blank, in that field. That was causing a lot of things to be sent to the bridge folder.

Strange thing, the filter has been that way for years, and it just started misbehaving a few days ago. I wonder if a change in the software made it do that.

Please download and install https://ftp.mozilla.org/pub/thunderbird/candidates/155.0.1-candidates/build1/win64/en-US/Thunderbird%20Setup%20155.0.1.exe if you are running 155.0 on Windows - it has a fix which has been tested. We would value your immediate feedback that it resolves your problem without introducing new problems.