I literally just got back into the game and I don't remember this being an issue. However today I noticed nothing was spawning especially trains etc like you said. I bought a train ticket and noticed absolutely no one on the train no armed guards no passengers nothing only to driver. I have a few mods installed like unlocking online content, open interiors, lasso mod, extended contracts and maybe one or two more I'm wondering is there a set limit and how much you can have before completely breaks the game. At this point Im property going to remove ones I really don't need and keep maybe one or two and best.