I've seen numerous BSOD's of unknown cause on 8.1 systems
Most have a 2012 version of the Intel Management Engine software/HECIx64.sys driver
I have recommended updating this - but cannot pin it down as the cause (because of the many changes that we make to the system when trying to fix BSOD's)
That being said, I have pinned it down as being the cause for many systems not being able to upgrade to Win8.1
Today at work I updated a Lenovo S400 Touch to the latest version (184.108.40.2068) on the Lenovo site and that fixed it (it was the only change that I made to the system).
The most recent version at http://downloadcenter.intel.com
I suggest scanning all 8.1 systems for this driver and updating it proactively.