Hi, after some research I found a clue about the reason. My host provider Siteground and the Cloudfare service has issues. After deactivating cloudfare I managed to update the theme and activated cloudfare back again. It worked somehow. Thanks though... This might be helpful to others.
In addition, a criticism from me, on forum pages, hiding content based on different products of yours is not logical since they share features and I couldn't access replies of a few questions because they belong to a different theme. I think forum restrictions should be based on whether verified buyer of any product or none and this will prevent duplicate requests on your end.