I don't know why the jet engine upgrade crashes your game. It works perfectly on my end. I can't trigger it to crash at all.
I will change the nanoshield so it no longer blocks lava. I've also fixed Mark respawning but I haven't uploaded that build yet, but I will.
62 days ago (+1)
I tried it on the old win 10 version and it does give me the "dash engine" without freezing.
Just to mention it and make sure, I was playing the current latest SAGE version (it's the version in which the freeze happens).
The screenshot is the text prompt when the freeze occurs.