Using the Jetpack mod while on auto-pilot causes the path lines to remain visible forever. They even persist through saving and reloading the game:
https://i.imgur.com/kyroqNW.png

The same happens when entering a train. Disabling/Loading/Saving/Re-enabling the mod makes them go away.

Same. I haven't found a reason yet. It happens without JetPack, and not near trains. I thought it might be Picker Dollies or Teleportation, but often happens independent of them. To clear them, I need disable the mod, play, save, then re-enable the mod.