It looks like this is fixed in the latest ACF release, as per patch notes:
*Release Date - 8 October 2019* * New - Added new choice "Add" to the User Form location rule. * New - Optimized acf_form() logic when used in combination with acf_register_form(). * Fix - Fixed bug causing incorrect field order after sync. * Fix - Fixed bug reverting the first field type to Text in Firefox version 69.0.1. * Fix - Fixed bug causing tinymce issues when changing between block modes. * Fix - Fixed bug preventing block registration when category does not exist. * Fix - Fixed bug preventing block registration when no icon is declared. * Dev - Added RegExp compatibility for innerBlocks.
I am currently downloading to verify locally.
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