I haven’t worked with F2 data at all but I’ve seen this with GNIRS flats. I’ve never tracked down the underlying cause but I’m usually able to work around the crash by changing the value of the lthresh parameter. I seem to remember that setting fl_vardq- can help as well.
I’m actually going on leave from Gemini starting tomorrow so I’m afraid I won’t be available to follow up with you. Good luck!