I might try TM:PE and see if I get the same problems. I did prefer Traffic++ to TM, so I'm more likely to test with T++V2 once the current problems and performance of that has been fixed. I have seen the same behavior with T++V2, so they might have the same problem.

Even though the dispatcher doesn't affect the path finder it can lead to service vehicles changing target more often, and in places where they usually wouldn't. This might make problems in mods that do replace the path manager (or in the original path finder) more apparent.

For example, the game usually assigns targets to service a vehicle when the vehicle is in the service building or has just serviced another building, but this mod may assign a target to a vehicle which is out driving more often. Whenever a vehicle is assigned a target, it will need to find a new path. If a mod makes path-finding slow, that could cause a vehicle to stop temporarily while finding the new path.

The next update of the game is likely to do this a bit less (as a side effect from other changes), but might still do it more than the original game.

If this keeps beeing a problem with traffic mods (or, especially, if it starts to become a problem in an unmodded game), I might have to change some stuff (including overriding more game code).