Hard to say for certain, it's such an intermittent thing and usually happens over THERE while you're working over HERE so you never see it right away. Apparently nobody knows the exact cause for certain, or has a confirmed faulty asset that will duplicate the gripe first time every time so it's impossible to pin it down. Undo/redo maybe, deleting baseboards maybe, what I found when working on the first Chicago Metro was level crossings that went spastic every time it happened, and the same ones also rendered phantom crossing bells 10 miles away from the nearest one sometimes. Got rid of all of them, no more phantom bells, didn't cure the screwy spline object completely but reduced it to the occasional "spline track that thinks it's a fixed track object" in small areas. Odd part about that is all four turntables on the route would vanish when I deleted the faulty track section using the scenery object tool, I still haven't determined if the turntable object was the cause or a victim of some other bug. These screwy spline track becoming fixed track bugs were happening miles away from the nearest turntable, so why the turntables were always affected by the deletion is still a mystery.
				
			 
	