Couldn't save any tags in 2.84a on Mac Sierra

I've been using mp3tag for many years but I haven't had this happen in any other version. I'm using 2.84a on a Mac running Sierra. The program seems to run okay, but when I add new data in a tag field and save the file, the new data is not saved. I've tried this with the files in two directories with the same result.

In past versions of mp3tag files in some folders were treated as read-only and you had to approve changes to the fields by clicking OK in the pop-up window. That isn't happening now. I see the "file saved" pop-up but no changes are saved.

Thank you for any help you can give.

EDIT: In order to write v3.3 tags, the option to write v3.2 tags has to be checked. Since I didn't want to write v3.2 tags, I unchecked that box. It wasn't what I would have expected, but that's what had to be done.

I am absolutely puzzled:
AFAIK there are tags of the following versions:
ID3V1
ID3V2.3
ID3V2.4

and APE.
So I wonder which MP3tag setting actually did it for you or are we talking about something completely unrelated to MP3tag?