I just found out, since this bug is popping non-stop in Cuhof cave, that on each tax tick, we found ourselves in and out of vehicule zone.
The restrictions comes on and off below the radar, as we move and make it tick - thing that we cannot see on logging screen.
I have no idea if this helps fixing it, but its an observation.
557 messages ~ Vehicules allowed
558 messages ~ No vehicule allowed.
And it carries on and off and on and off.