Hi @dbswebsite
That’s weird. Could you please try it in a single site installation? You can export the fields (XML), import it back in the single site and then upgrade ACF there. If the upgrade is successful, then you can export the custom field from there (JSON) and the import it to your live site.
It’s a lot of work, but I guess it’s OK for an emergency situation like this. I’m sorry for the inconvenience.
I’ll investigate this issue again later and hope I can give you a good news 🙂
