It seems like I can get this to happen reliably by i_timescaling to 10 and waiting at the spawn. It seems to be the issue is he does not actually take damage from the truck despite playing the blood and gib animations, either that or maybe he takes so much damage that his health rolls over.
I've seen this happen many times in the past. It's really nothing new. Gonna have to see if it is easier to reproduce now, but ultimately this is a typical result of CON's shittiness.
In all my recent tests on RR I have seen this only once, which I consider normal. It's just a poorly written CON script that cannot really be fixed on the engine side without replacing it.
RRRA has a fix for this that at least stops the endless gibs - but due to being too careful with enabling features across games it was not active in normal RR.
I just removed that check so hopefully this problem will be gone now.