I could have swore I posted a comment a couple of days ago on this… hmm, hopefully I didn’t post it on the wrong topic
I was looking at the export you sent and I think the reason you were having a problem is that the field keys are duplicate. Field keys must be unique and this is likely causing the issue when you save the field group.
Is ACF creating the duplicate field keys when you create a new field? Show the field keys and let me know if they get duplicated when you add a new field.
