An error occurred while saving the commentKris commented
Hi all, was having the same problem here and found a solution. Hopefully, this works for you too!
We had to open the .mogrt files IN AFTER EFFECTS on the computer of the person trying to use them. (To open a .mogrt in AE you have to jump through a few hoops of renaming extensions as .zip.... this premiere gal tut shows how... https://www.youtube.com/watch?v=t25C8McugXs_)
Once in AE, we just switched each text layer to a random font and then back to the desired one to help AE "refresh" and see the font correctly.
We then had to re-export the .mogrts from that AE (overwriting the existing file with the same name) and save them to "local templates folder".
Back in Premiere, everything worked well after that. No errors! It's a bit of a tedious process but it appears to only need doing once. Hopefully this helps.