Okay, The import tool for XML is really not that good to be honest with you.
The reason why you need to resave all the posts is because ACF uses an internal structure where each ACF field in the DB is paired with a “hidden” field which uses the structure of _field_name (the main field has field_name). These are probably not copied along with your XML file…
Also the reason why batch updating does not work is because it doesn’t actually update the entire post but rather looks for any settings you’ve set in the batch update editor and just updates those.
So I’m afraid your option is to either update each post manually, import them in another way or create a short script that updates the posts automatically. I’m not 100% sure the last option would work tho.
if you tell me the slug of your cpt I can probably create a simple snippet for you to test 🙂
