Most of the time, your grub is still there, even the link on your efi partiton. Only the evivars in uefi need to be reminded of their existance far too often.
Wow, the 4 regrettable shits. I can hear the sound of each of them. The warcries, the tears, the battlehorns; echoing through the stalls. The cheers of bystanders, united in awe and terror. The face of the warrior rising from the throne, blood-red and drenched in sweat.
If you consider the human brain works in 90 min chunks for most things including sleeping, that is completely within spec. For another chunk of sleep, you need to go to bed 60-80 min earlier.
I would conclude from this that your dc-dc converter is out of whack and only works stable enough for a small range of input voltages. This hardware issue might require a hardware fix at a repair shop :/