I was facing a closer problem, every time I publish a post, it shows “Validation Error” message, and all settings in the post won’t save. I found an action registered by “NextSripts SNAP” plugin that made this conflict with ACF Pro.
Under “NextScripts SNAP” Directory, open the file “NextScripts_SNAP.php” then find this line:
add_action('publish_post', array($nxs_SNAP, 'NS_SNAP_SavePostMetaTags'));
change to:
// add_action('publish_post', array($nxs_SNAP, 'NS_SNAP_SavePostMetaTags'));
Set “NextScripts SNAP” to publish using schedule instead of “publish immediately” and set the schedule to something small, I chose 3 minutes. And all the problems went way. I hope this solves your problem as well.
