Just checking in on this again. Hoping someone has an answer since I can’t seem to find the answer in the documentation.
My issue is tied to Jetpack. If I leave the theme alone but deactivate Jetpack, I can edit the ACF fields and nothing bad happens. But if I edit the fields while Jetpack is active, the fields vanish and I can’t create new ones either.
I am having a similar issue. I imported ACF fields into a new site, with content from three old sites. The fields are completely uneditable though, and I can’t create new fields in any way either.
I upped max_input_vars, and checked all settings, but nothing seems to help. I also removed the plugin and re-added. Any ideas would be helpful.