catalina – Bad font resulting in invisible text in email and elsewhere

Recently I started receiving emails with blank messages. If I reply-to those emails, select the text and change the font, the text shows up.

Via some experimenting I determined that Times Roman and Times Regular appear to be the problem. These are, I believe, system fonts. I’m running Catalina, all up to date.

I use Font Agent Pro to manage fonts. It doesn’t report any problems.

How should I go about repairing this?