EDIT1: the world editor solution works the best!
EDIT2: so, basically, indeed, it is a desync issue. if someone is smoking like crazy, you will have to stop and let people sync their edits and queues. if that doesnt help, ask them to press CTRL+R
ANOTHER SOLUTION is a bit technical and needs explaining. if your gearbox settings (gameplay assists) are set to arcade mode, it may affect every other car, including players! there are still a few gameplay settings that are not yet implemented in beamMP and may cause desyncs, one of them is ignition (start off) and brake temperature (start cold).
if you have a wheel (and a shifter):
Options > Gameplay > Vehicle Behaviour > Default Ignition State = ON (running)
Options > Gameplay > Vehicle Behaviour > Gearbox safety > Throttle and Clutch assist = OFF