Just fyi; updated from ACF 4x to ACF PRO today for one site, and had couple of wonky things
a) duplicate copies of all fields were created in the edit fields view for the single existing field group (very basic, about 8 data fields, several plain text, several WYSIWYG). Ended up with (3) copies of every field value, and luckily was able to simply delete the 2 duplicates for each field without damaging existing data in first field.
Free version was fully up to date as was WP, etc. Installed version of PRO latest version as of 8/25/16.
b) also note when making “copy” of an existing field group it defaults to “active” vs “deactivated” so one initially has duplicates as well in post editor. Likely “inactive” by default more useful when doing a backup of existing group on live site.
Just heads up. Thought I’d post here vs bugging you by email 🙂
Just to make sure, did you follow the steps exactly for upgrading? https://www.advancedcustomfields.com/resources/upgrading-v4-v5/
Especially the part about activating 5 before deactivating 4 and any add ons? you also should not do anything between these steps, like try to edit a field group.
If you follow the upgrade steps it should work. If it does not work then you should submit a new support ticket https://support.advancedcustomfields.com/new-ticket/
