I restarted my flight and my cockpit knobs were missing and black
This clearly proves it's nothing related to the scenery. You probably have just exhausted VRAM, and this has affected the scenery AND the cockpit graphics. They were both victims of graphic resource exhaustion, not the cause.
Something you want to check, is the HIGHMEMFIX tweak has been applied, and of course, lowering your graphic settings will reduce the chance to exhaust graphic memory.
Something that happens only after many hours, could be an add-on leaking memory, and the most likely candidates are airplane gauges, because they are the most tricky to program and contain actual programming code that can be bugged. A scenery is hardly a cause for memory leaks, since it doesn't contain any code (it's just polygons+textures), and whatever interactive code we run, we run externally from FSX in the Couatl.exe program, which means we can't cut into the FSX resources.
