That’s weird. Could you please make sure that there’s no conflict on your site? Could you please try to reproduce the issue on one of the WordPress’ stock themes (like Twenty Sixteen) with other plugins deactivated? If it disappears, then you can activate the theme and plugins one by one to see which one causes the issue.
Also, could you please make sure that you didn’t register the fields via PHP code?
If the issue persists, could you please open a new ticket from this link: https://support.advancedcustomfields.com/new-ticket? Please provide temporary admin credentials to your site and explain your issue again in that ticket.
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