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.
If the issue persists, could you please open a new ticket and provide temporary admin credentials to your site? You can open a new ticket here: https://support.advancedcustomfields.com/new-ticket. Also, please don’t forget to explain the issue again and provide the link to this thread.