Comment 8 for bug 1877052

I haven't seen any similar reports nor any updates here.
Might I ask if you have got any further since then?

Qemu 5.0 is available in Ubuntu 20.10 now, if you are willing to upgrade or install a test system that might be worth a try (new libvirt is still WIP, but unlikely to play a role here).
20.10 proposed would even have a 5.8.0.12.14 kernel since a kernel change might have been what started this that might be worth a check as well.