Convert Plus 3.5.17
Using above versions on a fresh install. So Convert Plus is the only Plugin, that is active.
Problem: Convert Plus does not save changes to a blank modal in FireFox. Convert Plus also throws an error in the console (see screenshot) in FireFox all the time.
However I also tested with a non blank templated, and I was able to save successfully. It seems only saving on modals that used the blank template saving is broken.
In Chrome no errors do appear in the console.