Problem in qemu was found. But I do not understand why it works in upgrade v47-->v48 and setting11-->settings12 and not with v48+setting12.

In /etc/default/mount-opts is KERNEL-POWER-HOOK line which run script /etc/kernel-power/pre-mount (if exists). But if this script does not exists it hangs too (WHY?) And why it does work after upgrade?