Cs-Cart Redirects To "under Maintenance" Page, After Some Actions

CS-Cart started acting out recently, after user registers he is redirected to "under maintenance" landing page, same happens when admin tries to delete or edit a user, editing is success, but deletion fails.

Same happens when admin tries to edit SOME of the products on the website.

What config should be the reason of this? This literally started yesterday and we have not made any new deployment to the server or config changes.

One of my new vendors has reported something very similar. Sometimes but not always when a change is made or attempted to be made and saves he is logged out. From the Admin side I don't have that issue