One more interesting piece of info is that on the s390x machine the qemu version is 3.1.1.1. But, on my x86 laptop with openSUSE Tumbleweed and qemu 7.0.0, I can reproduce the same success and failure when using qemu-system-s390x. I believe this is not a problem of qemu itself, but as I don't have a machine to install the problematic kernel and boot, I can't be sure. Any help to debug the issue is welcomed.