I can confirm similar issues post Security Update 2020-002 on a 2018 Mac Mini runnign 10.4.6.

- A few days later I power it down. On restart refuses to boot normally, taken to Internet restore, which ends in Error -1008F.
- After clearing NVRAM it boots normally.
- Left to sleep overnight
- In the morning, it had shutdown and on starting up normally I received an ‘Unexpected Shutdown message, the crash log showed a panic with iBridge.

Reported to Apple with Feedback Assistant