Well you obviously don't have a cpu failure, given the success with P95; nor a heat problem from the temps you are getting.
That only leaves the badly seated, which is unlikely because the problem is so sporadic.
Worth trying a reseat of your cpu and heatsink though. Clean off all the old thermal interface material from the heatsink and cpu with Akasa TIM Cleaner and rubbing alcohol. Reseat carefully using a quality TIM like Arctic Silver 5.
If you still get the problem I would suspect a failing mobo as cpus tend to fail catastrophically when they go.
However since you are in general getting stable performance, if you can live with the annoyance then I would wait until it craps out altogether and then replace your mobo.
TOG