Advanced Custom Fields Pro 6.4.0.1

Fix - Uploading multiple files nested in a subfield no longer causes a fatal error when using basic uploader

Improvement - JavaScript initialization performance while editing large field groups has been improved, especially in Safari
Improvement - Tooltips for field settings are now shown as inline instructions
Improvement - Saving a field group is now disabled until a field group title has been entered
Improvement - Additional sanitization across various internal parts of the plugin
Fix - Dragging and dropping a field in no longer opens the field settings in Firefox
Fix - Copying the field name or key to the clipboard now works as expected for new or reordered fields, and subfields
Fix - Saving a field group will now temporarily disable the "Save Changes" button while saving
Fix - Block templates that include html comments as the first DOM element no longer crash the block editor on edit
Fix - Block templates that include InnerBlocks on the DOM’s first level no longer trigger JS warnings
Fix - Block templates that render other blocks now correctly render their InnerBlocks
Fix - Legacy block attribute values are no longer overwritten by blank defaults of new versions
Fix - Paginated Repeater fields now work with non-paginated Repeaters as subfields
Fix - Repeater pagination is now properly disabled while inside blocks
Fix - REST API no longer causes a PHP warning if $_SERVER['REQUEST_METHOD'] is not defined
Fix - REST API now supports integer keys for the Select field
Fix - REST API now supports passing null to Image and File fields
Fix - Invalid ACF meta keys no longer cause a fatal error when retrieved with get_fields()
a11y - The Relationship field is now fully accessible for keyboard navigation
i18n - Select dropdown arrow is now aligned correctly in RTL languages
i18n - Radio buttons are now aligned correctly in RTL languages

Security Fix - ACF shortcode security fixes detailed here
Improvement - Field names and keys now copy to clipboard on click, and do not open a field
Fix - The field type input now has default focus when adding a new field
Fix - ACF no longer publishes h1, h2 or h3 CSS classes outside of the ACF admin screens
Fix - Conditional field settings now work correctly across different tabs
Fix - The field list for sub fields are now full width
Fix - ACF admin notices now display with correct margin
Fix - Admin CSS improvements when using ACF in an RTL language
Fix - Clone fields now have the presentation tab for setting wrapper properties when in group display mode
Fix - Appended labels on field settings will now be displayed in the correct place
Accessibility - The move field modal is now keyboard and screen reader accessible