Update, Feb 14 2020: this happens with macOS Catalina 10.15.3 also—complete hard crash.
Readers keep mentioning crashes with macOS Catalina. I’ve seen too many myself.
Here, all I did was try to eject an SD card—no response then the Mac Pro crashes. I don’t know what an “unexpected S5 entry” is. I just know that Apple has a pattern for years now of rushing products out the door without testing adequately.
This kind of thing is so unbelievably unacceptable—an OS should run for months at the least without trouble, as my servers running macOS El Capitan have for years—24 X 7 X 365.
I am not the only one seeing this problem as I found another baffled user on the web with the same issue.