I’ve looked at this further and did some more testing and these are the conditions that are needed to cause this error.
1) restoring a page revision, no other post type causes this
2) the WP main content area hidden by the use of “Hide on screen” for a field group
3) The value of an ACF field that is being restored is an array
I have tried debugging why this might be happening, but I can’t figure out what could be causing it.
My only suggestion for anyone seeing this is to contact support https://support.advancedcustomfields.com/new-ticket/
