<input class="input-alt" type="hidden" name="fields[field_520cffb7446d5][field_520cffc9446d6]" value="">
The entries still have values in the database, so the data is there.
We’ve updated to the latest version of ACF, tried creating new entries to see if they would save (they do not), and tried creating a separate field with default datepicker settings.
I am experiencing a similar issue. Have you had any leads?
The issue I was having was caused by $(window).load() not firing inside of ACF’s inputs.js
There wasn’t anything actually wrong with the plugin itself, but there’s an incompatibility with WPMU Dev’s Help Videos plugin (or any other plugin that ALSO declares a $(window).load() as subsequent calls to $(window).load() override previous ones).
Hope that helps.