This issue occurs mostly because you have a field group registered via PHP code. Could you please try to do the upgrade on one of the WordPress’ stock themes (like Twenty Fifteen) with only ACF activated?
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Accordions are a great way to group related information while allowing users to interactively show and hide content. In this video, Damon Cook goes in-depth on how to create an accessible accordion block using ACF PRO’s Repeater field.https://t.co/RXT0g25akN