linux reboot causes a short power off - can I prevent it?

I'm using Ubuntu 16.04 (systemd!), keel 4.4.0-24, on an Asus N3150I-C MB, with a Kingston SSD, which contains /boot /efi and the rootfs's volume group and a WD Red HDD as backup device. I noticed today, the Unexpect_Power_Loss_Ct in SSD's S.M.A.R.T. attributes increasing at every reboot, but not if I shut it down with the command "poweroff". And really... at reboot, the machine looses the power for some seconds, (I hear when the heads of the hdd go to parking position with a loud snap) then switch itself on again, and boots. If I stop the boot at the grub menu, and try to restart it, by pressing Ctrl-Alt-Del, the PC just restarts without switching off the power, so IMHO it's not a hardware issue. I experienced the same problem with older (3.x and older) keels, but not with keels 4.x until today. How can I prevent this power loss? I can't find relevant information in the logs, though I changed log level to debug (I set keel parameter systemd.log_level=debug)

I suspect, perhaps some parameters (APM, ACPI etc) changed in the latest keel, but it just an idea. (I'll try to check it)

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