I have not seen this on any sites running any of the themes or plugins that I use. I would guess that there is some incompatibility issue. But there really is no way of telling exactly what happened or why the field names are missing.
If you did a backup I would first restore both sites.
If you can’t do a restore, look in the DB, search the posts table for post_type = acf-field and look at the post_excerpt column. This is where the field names are store. Make sure the field names are still there and look correct. If they are not then, well, you’ve got huge issues.
Then (or starting here if you cannot restore) I’d start with basic troubleshooting, deactivating other plugins and changing themes to see if I could narrow down where the problem might be.
