Comment 8 for bug 1847806

Trying to help with the cpu type here - the default for the mentioned config will be:
/usr/bin/qemu-system-ppc64le -name guest=ubuntu19.10-ppc64le-test,debug-threads=on ...
  -machine pseries-eoan,accel=tcg,usb=off,dump-guest-core=off ...

Without an explicit -cpu option set.

The libvirt XML just has no <cpu> section as all.

The default qemu picks in that case in the past was:
PowerPC power8_v2.0 PVR 004d0200
PowerPC power8 (alias for power8_v2.0)

Checking the qemu code shows:
4363 static void spapr_machine_3_1_class_options(MachineClass *mc)
4370 mc->default_cpu_type = POWERPC_CPU_TYPE_NAME("power8_v2.0");

With the code we can map this
(qemu versions go into the machine type, so xenial would be 2.5, bionic 2.11, ...):
new: power9_v2.0
<3.1 power8_v2.0
<2.7 power7_v2.3

So in the setup here it should be power9_v2.0 while in any release before Eoan it would have been power8_v2.0.

I'd expect P9 should be P8 compatible, but maybe that helps in debugging this.
Downloading a ppc64 image for testing on my own ...