Apple Mail content is blank for 20-30 minutes

iMac with Monterey

For quite some time I have been having issues with Apple Mail.

First, I constantly have to use the "rebuild mailbox" feature as message titles, senders, and content were frequently mismatched.

Now, when a message arrives, it will appear in the preview pane but when the email is selected the header is correct in the email but the body is blank. If you leave this email selected the body will suddenly appear after 20-30 minutes.

I run Bitdefender (as well as CleanMyMac) on both my iMac and Macbook Air. For some reason the Air doesn't have this issue.

Apple "support" has blamed this on "outside non-Apple Apps-they specifically point to Bitdefender and CleanMyMac as well as others and they suggest "these apps should be deleted and simply to rely on the Apple software. Yeah, that's not happening. Bitdefender has saved my bacon too many times.

I'm asking CleanMyMac about this as well.