Hi and welcome to our community 
Is your ubuntu starting shutdown process (clean stop) or directly power off like electrical power lose on desktop computers ?
I'm fixing broken hardware in my free time at my work and got something similar on a Thinkpad t460.
The solution was to unplug the power supply and the external battery, unplug also the secondary battery embedded inside the computer, also, unplug the cmos, press 30sec power button (it will do nothing as there are no battery). Assemble everything back, set up the date inside the bios and i got rid of the issue.
For me, it looks like a CMOS issue - do your computer travel in time ? xD
Good luck