Should have updated... I’ve been working with the SoftRAID development team, and they were able to recreate the issue easily. This should get fixed in 10.14.4 if we’re lucky. It’s nothing to do with SoftRAID etc, but just - as you said, a product of drives taking too long to shut down - causing issues.
Interestingly, I’ve been able to recreate the issue on a 2014 Mac mini and a 2012 Mac mini, but those minis don’t actually generate a crash report, despite shutting off HARD during the system-shut-down procedure. The 2018 model is the first model of mini that actually complains about the problem.
This is great info! Thanks for updating the thread.