Can you recreate an example of either/both of the above situations in JV-ODE
I can - I have been working with the cardemo.bb program that comes with the wrapper, modifying it a bit to try to get the car racing over one of my SRX stunt racetracks, and I've broken the simulation lots of times - undoubtedly some were down to a poor choice of numbers setting up masses etc.., but quite often the simulation would let me complete a lap or so, then explode at an unexpected moment.
I'll see if I can find an example setup that crashes often but randomly to send to you.
The main gameplay problem seems to be trying to make the car not flip end over end after landing from a jump, but I haven't tried your tip of using the geomtransform yet - I'll try that tonight and let you know how I get on.