I have read the following Threads, but no one could solve my problem!
Sorry, but in all those threads, users eventually found the solution, which was always caused by either the Compatibility mode (not JUST FSX, but any add-ons that runs with it in Compatibility mode might cause this ), or a problem with video drivers settings or tweaks.
There are no other known solutions, because it's not a problem of the scenery, and none of the users that solved it in all those threads solved it by any other method than acting on those external factors which affected the scenery.