Do you use ACF in combination with WPML for your project? If so, I might be able to help you.
I found out the problem for me was that I set my WP lang. to nl_NL (Dutch), my default WPML was English and my strings were Dutch.. WPML bugged on that and this gave lots of conflicts. ( fairly new to WPML )
After doing a complete removal of WPML and re-setting everything, it worked flawlessly.
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