Sounds like turbo boost boosted the clocks beyond spec after the new microcode for Haswell got applied. Ivy Bridge to Haswell is more affected by the new microcode for Spectre and Meltdown and increased system stress beyond what it used to be.
You’ll need to boost voltages and permanently enable “performance” governor. Turning off Turbo locks your processor to it’s slowest base clock, so while it helps stability, you lose all the performance your processor is capable of.
Do an FFmpeg encode as the stability test, you’ll quickly find instability even at stock.