I have experienced a similar issue (or at least related to caching). In a new website with the latst ACF Pro hosted in Siteground, activating their own caching plugin called SuperCacher breaks the ACF UI and all field group appear as inactive. Removing the plugin does not help, you have to also remove the object-cache.php from wp-content and delete the cache folder. I suspect the issue was because i enabled memcache but i am not 100% sure. This might be relevant to the above question
