Q: Mail 9.3 prefs change spontaneously

I am using Mail 9.3 (3124) on a MacBook Pro with OS 10.11.6. Suddenly, this morning evidently, the prefs for my account setups started going wrong. A couple accounts' ports changed to 587 from 465.

Then, as I checked to make sure that all was well, I noticed that for some, the configuration for Port 995 changed too. The checkbox "Allow insecure authentication" is s'posed to be checked, but the box keeps unchecking itself. It appears to be random which accounts do this.

Is there anything I should try, other than trashing the prefs?