I started a new city, residential area with some houses along T++ pedestrian roads. I switched to a different city a then went back (load from the ingame menu, not exiting the city). After a while I noticed that service vehicles (notably garbage trucks and police) ignored the pedestrian roads and stopped using them, they were using them before just fine...After restarting the game all works fine. So maybe a mod incompatibility (I use only compatible mods though) or just a weird glitch in the pathfinding...hope it helps someone