I tried later in the day, and the issue is still there. It does seem to be coming from TB 142.0. As I noted, I have seen somewhat slower loading of emails for the last several versions. For example, I would delete an email. While the email did disappear from the list right away, and the previous email opened, I saw the lower right bar from the activity manager activated for a minute or so. I also noticed that, if I try to compact files while the lower right bar shows activity, the compact process takes much longer. Even with 142.0, the process does eventually work as it should.

Since I really cannot work with this, I restored to TB 141.0. It gave me a error that I was using an older version on my profile. Just to be safe, I restored the profile as it was on 8/20 before I made the upgrade to 142.0. After the restore, I am back to the performance I had before. I am sorry I could not provide more information as I am only a moderate skill when it comes to software, and I was not sure what else to look for or try.

Help. I started having the same issue with TB 141.0 today, even though it had been working fine. This time I am getting authentication errors with imap.google.com. Of course, it has been working fine. No changes were made since I turned of the computer last evening. I tried reinstalling TB 141.0. That made no difference.

This is disparate. Every time it tries to load a message it takes forever, apparently because of the authentication issues. This make TB usable.

I thought this might be a Bitdefender issue, since Bitdefender apparently made a major update this morning. However, I have listed the thunderbird.exe folder as an exception in Bitdefender -- and that does not seem to have helped. I did file a case with Bitdefender, and I am waiting for a response.

I have now confirmed that this is mostly a Bitdefender issue. Listing Thunderbird.exe as exceptions, suggested by the Bitdefender team, did not make any difference. Bitdefender does not have a way to pause all activity, like my old Kaspersky did. However, after turning on and off various settings, I found that changing the last setting under Online Threat Prevention to "Don't Scan Emails" seems to have corrected the issue. I still see a few slow responses from time to time, but that might be Google.

Having said that, it seems to me that the protocols used within Thunderbird to access IMAP email and various other activities seems to have changed in the later versions of TB, past around 128. I just seem to see a lot more activity, including authentications, when I do things as simple as delete one email and go to the next. Perhaps these actions by TB are necessary to insure proper syncing, but I just wonder if there might be less verbose methods that would be faster and perhaps also less prone to trigger reactions from things outside Thunderbird like AV.

I still have a case open with Bitdefender to address the slowing email issues.

I still have a case open with Bitdefender to address the slowing email issues.

Sorted out I hope?

Yes. I found that setting Bitdefender to not scan emails was an effective workaround. Shortly thereafter, Bitdefender stopped causing issues even when set to scan emails. I still seem to see a lot more interaction taking place to keep up with IMAP than I used to see on older versions of Thunderbird. It causes delays of a minute or so from time to time, but nothing like I was experiencing before with Bitdefender. I think Bitdefender was just slowing down all those different communications.