When two trucks are winched together, the tires, truck body, and trailer (if one is attached) begin spinning through themselves. They will continue to do so until the trucks are completely damaged and will pass through trees, destroying them and causing them to also do the same spinning through themselves.
Video: https://youtu.be/_naBmrCrPOs
I could not force this bug to happen after several attempts of winching two trucks together. It might be random, but it did happen twice in a single play session, causing me to have to restart the map. Exiting the game does not make it stop, nor