Can we see your cpuz with cpu and memory tabs opened at load?
If it's very random and impossible to reproduce I would start by resetting your gpu and cpu to stock then overclock one aspect of each (core/uncore/ram for cpu and core/ram for gpu) and take it slowly.
Try to work your way up over a few days, without an error code it's going to be hard to narrow it down. The best method would be to start over and change only one thing at a time until you find the one adjustment that reproduces the issue.