Mac mail messages appear blank
A couple of months ago I started having this problem where the content of certain email messages appeared blank in my Mac Mail browser. The subject would show up, but none of the content of the mail (although occasionally attachments do arrive, without any accompanying text). The weird thing is, the problem seems to be getting worse. It used to be just one or two emails per week, usually those sent to a list; now it's three or four per day, at least, including those from people/sites that showed up a week ago.
Note: I can see the messages fine in iOS mail and when I forward them to myself from iOS, I can then read them on my laptop. It's a workaround, but a pain in the axe, too.
Based on previous threads I've tried checking and unchecking the "Protect Mail Activity" box in Mail-->Preferences-->Privacy. That seems to have no effect. I've also tried "rebuilding" the mail boxes. That didn't help, and may have been what made it worse.
Other suggestions? Please? Anyone?
MacBook Pro 13″, macOS 10.15