wolfgang, qm showcmd 19250 run as expected with no error. Either VM running or not.
root@ohber-pve-01:~# qm showcmd 19250 --pretty
/usr/bin/kvm \
-id 19250 \
-name ohber-srv-01 \
-chardev 'socket,id=qmp,path=/var/run/qemu-server/19250.qmp,server,nowait' \
-mon 'chardev=qmp,mode=control'...