We’re seeing a similar issue when calling update_post_meta() or the ACF update_field() function from /wp-admin/post.php
If I delete any records from the database related to a given wp_postmeta field, then update_field() will work properly, but if I call it repeatedly to update a post’s meta data then it will retain the previous value.
I sanity-checked it by deactivating the ACF Pro plugin, and then it worked as expected. When I reactivated the plugin, the problem returned.
