I was not able to reproduce your problem.
Did:
paul@jacko:~/hurd1905$ sha1sum debian-hurd.img.tar.xz
1fe25529095a30d5b8fe7c889566f6af56ae41cf debian-hurd.img.tar.xz
Each time I try to launch, I erase the old .img and:
tar xJf debian-hurd.img.tar.xz
resulting with:
paul@jacko:~/hurd1905$ sha1sum debian-hurd-20190705.img
332c6ae2ca9ebc8d01c429b0f9dfebe625800e21 debian-hurd-20190705.img
paul@jacko:~/hurd1905$ kvm --version
QEMU emulator version 5.0.0 (Debian 1:5.0-5ubuntu9.4)
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
I suggest you try:
kvm -m 1G -smp cpus=1,cores=1 -drive file=debian-hurd-20190705.img,cache=writeback
or:
kvm -cpu help
have suggested me to try:
kvm -m 1G -cpu 486 -drive file=debian-hurd-20190705.img,cache=writeback
which works for me.