My personal shuttle train get the triangular "stuck at signal" icon every time it arrives at a temporary stop.
I click it so it goes away but it comes back every time the train is stopping.

Don't feel like going through the source to find a probably cause but it would be nice to not get that over and over again.
I am sure restarting the game would make the issue go away but that's not going to solve the issue, there's probably some stuck variable someplace.

The problem goes away when arriving at an actual station it seems.

I can't reproduce it. Are you using any other mods that do "something" with temporary station?

I stuck a train on a signal until the alarm appeared the first time, then made it go to a few temporary stations without the alarm reappearing. Some quick debug messages suggest the alarm got properly reset when the train left the signal.

Only train related mod i know i am using is LTN.
And as i said, it unstuck itself when i put a real station in the orders and stopped there. Didn't consider it until i wrote the report.

Not sure how to reproduce because it just happened out of nowhere.

EDIT: And the particular train has never stopped at a station before. I also leave the game running 24/7. So perhaps it happens once in a blue moon because of some overflow.

I guess that's 1 / 0 magic then.
Let me know if it happens again and I will take a closer look. But Fat is due for an overhaul anyways, so i don't want to spend too much time digging through 2 years old code.