I just spent way too much time figuring this out, so maybe this'll help someone out there. I installed the newest version of Gravity Forms Multilingual on my staging site, and translated some new forms I have been working on. I couldn't for the life of me figure out why the translations were not applied to the forms. Later found out they weren't applied to my existing forms anymore, either.

Turns out the newest GF ML plugin isn't compatible with the latest production version of WPML and/or String Translation. I had to update to the beta versions (5.1.0) in order to solve the issue.