Well, I found something right away when loading the savegame: seems it couldn't find an engine to build. It selects the newest available rail type, which in this case is monorail and with 2cc, that has no cargo locomotives. I think that's fixable
Also: it's not very happy about a map with so little towns. It picks a random tile, evaluates whether it can connect at least three towns if it were to place a crossing there, and if not, picks another. This went on for several months before it managed to find a tile that meets the criteria... I guess I'll have to extend the maximum distance it'll search for towns, since I don't really want to remove the randomness. It would be much more competitive if I did, but then it wouldn't play as nicely with multiple ChooChoos in the same game. Choices, choices...