Just updated GravityForms to 126.96.36.199.1 (seriously, wtf).
When Shadowbox is activated forms can not be edited or saved in the admin. I get this bug in chrome inspector.
Uncaught SyntaxError: Unexpected token < tw-sack.js:1
It's completely possible this might be something on GF's end, I just wanted to post the issue here in case others run into it as well.