Hi all,
another (hopefully) former victim of Security Update 2020-002 here. I was struggling with frequent crashes during sleep since the end of March (Mac mini 2018 with Mojave 10.14.6), ended with Amphetamine set to indefinite awake session. Two days ago I tried the Big Sur route. Signed up to the Apple beta software program, downloaded Big Sur public beta (12GB), installed it on my external USB drive and then put it back to the drawer. During the system installation T2 firmware was upgraded from 17P6065 to 18P50347c and Boot ROM version from 1037.147.1.0.0 (iBridge 17.16.16065.0.0,0) to 1554.0.0.141.1 (iBridge: 18.16.10347.5.3,0).
Anyway, after booting back from Mojave, it's been two days of fine sleep without any problem now. It looks to me that it also resolved two additional annoying issues I had:
1/ my Wacom tablet was unusable for about 10 seconds after every wake-up (frozen pointer), and
2/ I had frequent spontaneous wake-ups of the computer during the sleep (even with Power Nap, Wake for network access, Find My Mac and other suspected processes turned off).
Now both issues seems to be gone as well. Let's hope that my long-term report will remain unchanged.
Many thanks to all trying to solve this frustrating problem and especially for the Big Sur beta tip!