I was able to get all of the vehicles stuck, ie thrown tracks, in Rotar's scenario. It didn't happen at the same time and one vehicle went through the all of the fences fully three times before something happened to it. I think that there is a chance that it could happen at any time, but does not happen all the time, for each vehicle. I was a participant in a multiplayer session where one of the tanks threw a track when it went through a single strand of concertina wire for the second time so I know it can happen in game.