If a train is cleared of its scheduled stops, the train limit for the last cleared stop does not get reset. As a result, it is possible to create the situation in the image, where the "test" station is full despite having no train assigned.
It took me a few minutes to find the culprits, since there is no way to find those trains from the train menu.
Looks like the train is still occupying the station block, does it still occur if the train is not in that rail block?
Yes, it doesn't matter, see below.
I discovered the issue when I wanted to send freshly constructed trains from my mall, but changed my mind before they received fuel from the drones. 2h later my production stopped to a grind because no other train could reach the steel depot.
Thanks for the report. I see this issue was already fixed for 1.2.0 and because i am considering this to be minor issue i do not want to fix that in 1.1.x due to possible merge conflicts (that fix would be basically a temporary fix for 1.1.x only).