The only thing that ACF stores about the field in the DB is the attachment ID.
Everything else about the field is stored as a serialized array in post_content with a few items put into other fields for the post and a couple of meta values. Any problems with this should be evident when you’re editing the field group with the effected fields. What are the settings on these fields? (old ones vs new ones). Are you able to look at any differences of the fields in the database?
