When playing this scenario I get stuck at the siding where I have to decouple my consists and move on.
I can't decouple anything, and my train doesn't move anymore, not even when applying full power.
You may have stopped in the wrong place, you have to stop at the tiger point to unlock the decouple command. I have not run this in years but I did run it a lot as a beta tester and can say that it can be run to the end in UTC and TRS4.