Qubes OS if very unstable in my case. Unfortunately, I’ve had enough, I can’t recommend Qubes.
First, desiring to get rid of the reboots, I changed my RAM, CPU, motherboard, and power supply. Now I understand that the problem is in the OS. It’s crashing without any signals in the log, mainly on virtual machine start/stop.
So I still can’t boot into the system at the first time! Usually I am trying to boot five or more times to start all my appVMs. Then I am trying to keep my computer uptime 24/7, that is usually a week without the accident reboot. Starting an appVM turned into a reboot lottery.