I'm pretty confident the 'crashiness' has to do with the amount of power being drawn.
I'm thinking the USB2 SATA drive works OK because it draws less power from the USB port than does the USB3 NVMe stick.
What makes me think this? Well, the USB2 SATA has been stable, but I just plugged in a USB SDR (Airspy HF+) into the Pi 4 and it crashed instantly and repeatedly. Then I plugged the Airspy into a powered USB hub plugged into the Pi 4 and everything is happy.
Also to explain why the USB3 NVMe was happy with the old 32-bit OS, I believe the 32-bit OS was not driving the Pi 4 as hard so it was drawing less overall current, making more available for the USB ports. Actually there were a few times the 32-bit OS crashed when doing big software builds but I thought it was because it was running out of memory, but now I think it was drawing too much power.
So, I think there is some tipping point of power drain that makes the Pi 4 crash.
I am working at my home station so the sbitx is getting plenty of 12 volt juice, the PSU is good for 30 amps.
It seems if I want to use USB3 NVMe then I will have to hang it off a powered USB3 hub instead of connecting it directly, but for now I am doing OK with the USB2 SATA drive.
Why do I bother? Well, my basic measurements show that USB2 SATA is about 10x faster in read performance than sdcard, and USB3 NVMe is about 30x faster than sdcard. It doesn't matter much for using the radio as a radio, but it does matter when you are developing software on it.
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Regards,
Dave, N1AI
Dave, N1AI