Any gates that were left unlocked near the truck that could swing open or doors nearby that can swing open and touch the car? I had my car locked away in a corner of my base, but had a gate that wasn't locked and a metal door to the building, since some of those randomly open sometimes, when with a server restart or player proximity, it swung open, pushing the car just a bit into my gate and upon server reset my car was gone, happened right before my own eyes.

Not my base but it was a prime example of how they are using fire places to build stairs. My base was in a building in solnichy.