My new Samsung SSD was causing strange lockups. Everything worked fine during the lockups except for disk activity. I found https://odd.blog/2013/11/26/yes-finally-fixed-ssd-freezing-computer/, which gave me a fix: make sure the IDE drivers are enabled, then change the drive mode from AHCI to IDE. It’s been a week or two problem-free!
Samsung 860 EVO
Biostar A960D+ mobo (AMD chipset, which is apparently the issue.)