It's honestly hard to tell. I changed the editor from Advanced to Classic and hit save. I got the error message, but upon trying to translate, I was using the Classic editor. I went back to settings, changed back to the Advanced editor and hit save, got the error, went back to translate and was indeed using the Advanced editor again. So that would confirm what you're saying as well.
On the other hand, I went down to Post Translation Types, set the "Glossary" type to "Translatable (only show translated items)", and also tried "Translatable (use translation if available or fallback to default language)" and tried to translate a page I have glossary entries for but the "glossary" post type/tag and related items don't show up.
The Glossary plugin allows for Tooltips and an encyclopedia style glossary on a website and is tested to work with WPML, another reason I chose WPML to begin with.
So I'm not sure what's going on here.
I appreciate the confirmation that the settings do seem to be saving on some level. But it's not working the way I thought it should.
That said, it seems like the ball is in my court now. I will try two things and circle back here:
1) Contact WPML and Glossary and see if they have any insight to the false error message and lack of Glossary translatable items.
2) Try Translatepress, it was actually my first choice and the theme and plugin support teams for what I am using all said "should work but we haven't tested it, let us know if you try."
Again, I sincerely appreciate the help and I will let you know my findings asap so we can wrap this up.