Bots deploy from my crawler robot train once upon stopping, then never again unless I move the train. I have about 600 "missing material" alerts around the map if that's relevant. Really looking to get a train that can actually build stuff!

That is relevant. Connected or not, your construction roboports share a single construction manager that iterates through ghosts at a limited pace, and the more ghosts you have on the map the longer it may take for construction robots to be dispatched. 600 "missing material" alerts are a pretty strong indication that your construction manager is overloaded and will not dispatch bots in a timely manner.