I had some places where the train stopped for a red signal but never proceeded - Locks Session. There was no obvious culprit. Today I was following the progress of a session on the information line at the bottom of the screen. I saw a red signal coming up but the nearest real signal was green. HMMMM, an invisible signal. The train stopped and there beside the train was a whistle post. I disabled all of the original issue whistle posts and now the place where the train always stopped was passed thru as it should be. There are other newer whistle posts that are not in the route and I did not alter them.