Quote Originally Posted by MgFrobozz View Post
At the time of the lockup, there was a blast of NULLs written to the log
If you by this means that there was a lot of bytes with a value of 0x00 written to the log, this is usually caused by a hard reset which causes the log-file not to be closed properly. The null's are reserved space prior to a file write / file flush from memory which is interrupted. When the system boots after a hard reset the syslog may have entries which states something about a dirty volume which has to be (and is) cleaned before continuing because of the hard reset.

If your problem is a resent issue started for no apparent reason, then I would guess that it is hardware related. The most obvious culprits are a faulty system drive causing corruption in the system / initramfs (check S.M.A.R.T. data for the drive for bad or pending sectors) or faulty memory modules (check with memtest). If none of those gives any clues, the next thing to check is the GPU and the PSU.