VM guest sometimes hangs on reboot in host xubuntu 22.04

If I reboot a QEMU/KVM guest, particularly after software updates, it sometimes hangs. The screen in Virt-viewer goes dark and the mouse pointer flickers; guest CPU use is high, sometimes 100%.

The only way out seems to be to force stop the guest and then start up again. This is mostly an inconvenience with Linux guests, but more of a concern with Windows 10. (No problems so far, but that could change at any time.)

I have tried using remote-viewer instead of the built-in Virt-Manager viewer, and connecting to Linux guests directly with ssh, but the problem occurs there as well, though not all the time.

I previously ran these guests on a Xubuntu 20.04 host without ever seeing this problem. The current Xubuntu 22.04 host is a fresh install, not an upgrade.

Virt-Manager version: 1:4.0.0-1
qemu-system: 1:6.2+dfsg-2ubuntu6.4
kernel: 5.15.0-48-generic #54-Ubuntu SMP Fri Aug 26 13:26:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: virt-manager 1:4.0.0-1
ProcVersionSignature: Ubuntu 5.15.0-48.54-generic 5.15.53
Uname: Linux 5.15.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: amd64
CasperMD5CheckResult: pass
Date: Fri Oct 7 17:02:56 2022
InstallationDate: Installed on 2022-05-08 (151 days ago)
InstallationMedia: Xubuntu Core 22.04 - amd64 - 20220421
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_NZ:en
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_NZ.UTF-8
 SHELL=/bin/bash
SourcePackage: virt-manager
UpgradeStatus: No upgrade log present (probably fresh install)