I’m also getting these warnings when trying to restore revisions on a custom post type (also with the main editor hidden via ACF). Two versions I can verify display this problem: 5.5.10 and 5.5.14.
This is all because of a more primary bug I’m trying to troubleshoot: restoring revisions on custom post types seems to succeed, but all values in ACF fields stay the same instead of reverting.
I’ll keep at it and post if I have any further info on either of these (what appear to be) bugs…
