The first thing I would try is resetting the System Management Controller (SMC), as it's responsible for power management, sleep/wake/hibernation, restarts/shutdowns, and so on.
Resetting the SMC on a 2018 model Mac mini
For your particular Mac mini you'll need to follow these steps:
Fully shut down your Mac mini
Press and hold the power button for at ...
My computer was also failing to shut down or reboot properly from being logged in with essentially the same crash message. The issue started happening after updating to 10.15.1. After resetting the SMC and also NVRAM the issue seems to have gone away.