6.0.20: Guest and Virtualbox Manager window unresponsive: audio problem when monitor goes to sleep?

[folj]

Hello. Today I noticed my Win10 VM that I run fullscreen on a TV used as a secondary monitor was completely frozen when I unlocked the host.
The window of the guest & the VB manager did not respond to clicks, so I had to kill the VM tasks, logout & restart the host. This has not happened before, so I attach the log of the run, and for comparison from when I reran the VM just now. The log ends about 90min after I locked the screen of the host, with messages about DSoundAudio - is this relevant? About repeatability: I do think I have locked the host screens since adding this secondary monitor, but I haven't seen this problem before.