Comment 7 for bug 1834113

Rebooting the guest when this is happening does not fix the issue, for what that's worth.

Last upgrades before this happened are:

Start-Date: 2019-06-20 23:46:55
Commandline: apt dist-upgrade
Requested-By: a (1001)
Upgrade: intel-microcode:amd64 (3.20190514.0ubuntu0.19.04.3, 3.20190618.0ubuntu0.19.04.1)
End-Date: 2019-06-20 23:47:11

Start-Date: 2019-06-24 08:23:45
Commandline: apt dist-upgrade
Requested-By: a (1001)
Upgrade: snapd:amd64 (2.38+19.04, 2.39.2+19.04), firefox:amd64 (67.0.3+build1-0ubuntu0.19.04.1, 67.0.4+build1-0ubuntu0.19.04.1)
End-Date: 2019-06-24 08:24:00

I also see a bunch of updates to libvirt on 2019-06-19.

Should I try downgrading intel-microcode?