19.04, 19.10 guests on 19.04, 19.10 guests.

VBox is locking up the host at random times -- at startup or while reading from or writing to host -- various times. The journal repeats the error in the title over 100 lines or so but there is nothing that explicitly expresses distress.

I am running VBox in the same configuration without error on another machine so there is something about this machine. One difference is this troubled machine has NVIDIA but switching to the Nouveau driver or changing NVIDIA version does not solve the problem.