Hi Robert,
Looks like you are right.
Sometimes? the vibration is clearly audible. In that case, I also hear an acoustic signal and select that option in the app. I don't know if the devices are designed that way on purpose, or if one of them was defective.

As for a possible change to Street Complete: Maybe local images of the traffic signal could be added so that users can select the correct one? Or the "quest_traffic_signals_sound"-question could be hidden or automatically answered in Zurich, if only the Zurich-standard vibrating signal is used here.