I use 5 laptops from this era regularly to frequently: i5 and i7 X220, i5 and i7 T420, and quad-core i7 W520. All are 100% stable and run for days on end with

I use 5 laptops from this era regularly to frequently: i5 and i7 X220, i5 and i7 T420, and quad-core i7 W520. All are 100% stable and run for days on end without a problem with Ubuntu, Pop OS, FreeBSD, and most other things. I think you may have hardware problems.