Is it possible to get an un-minified version of the JS used to generate the modals? I’d like to take a shot at debugging this as I’ve done some work previously with customizing the Media Manager modal.
The issue only occurs if you first open the Media Manager in the standard WYSIWYG and select Upload Files, then close that Media Manager modal. Then, when you click the Edit pencil icon on an image field you see the same Upload Files modal screen rather than the Edit Image screen.
The error was on my end. Turns out the theme was creating the field directly in the functions.php file rather than through the ACF admin.
The version I was upgrading from is: 3.5.8.1
I’ve also found a group where the admin displays 3 as the total number of fields but when I go to edit that group, only one shows up (the only field of type Text). If I then clone that group and edit the new cloned version, I can see the other fields that were missing.