I had a similar problem that looked to have been from upgrading from version 5.2.6 to the latest 5.3.7.
After the upgrade I noticed that whenever I updated or added a new field in ACF it would disappear from the listing of fields. Looking in the DB it was getting recorded in there but the post_parent field was recorded incorrectly so it wasn’t coming up on the ACF I was editing.
I also noticed it happened when I rolled back to the version before 5.3.7, I’m not sure how many other version it would occur in as I needed to get things back up and rolled back to 5.2.6 after that.
Have any idea why that could be happening to me. Maybe there is another plugin messing with that field on later versions?
