Elliot,
I think I narrowed my issues down to WP Engine. I’ve been troubleshooting for a while thinking it was an issue with ACF Pro, as I was having issues even when the Twenty-Fifteen theme was active and the only active plugin was ACF Pro.
As I mentioned before, downgrading to WP 4.0 from 4.1 seemed to resolve the issue, but that’s not an ideal long-term solution. So, for the short-term, I downgraded to 4.0 then cloned the site to WP Engine’s staging server where I could continue to troubleshoot.
Once cloned to their staging server, I updated WP to 4.1, assuming it would bring back the issues I was having so that I could use SCRIPT_DEBUG to narrow down the issue further. However, once upgraded to 4.1 on the WP Engine staging server, everything seemed to work fine. I cloned the staging site back to the production environment and the issues came back. . .so, I’ll be opening a ticket with WP Engine to see what on their end is causing trouble.
When I use SCRIPT_DEBUG on their production environment, I don’t see any errors in the console. . .but when I turn off SCRIPT_DEBUG, a lot of things that rely on JS in the admin fall apart.
Thought this might be helpful in case any of the other folks having issues are also on WP Engine.
