I used to use two lab grade thermometers that gave very close readings. One was NIST certified (with serial number), the other was NIST traceable. I suspected something was wrong, so I used water baths to determine how far off. Boiling was off 12 and 10 deg F high respectively, ice water bath (correctly done) was 4-5 high on both. talked myself into getting a Thermapen and confirmed they were both 7 deg low at a 150 mash temperature. Those things were all over the place. The Thermapen also confirmed my Ranco probes and ice bath numbers.
That means you were roughly between 130-134 for the 30 minute beta rest. That's in protein degradation temperatures, and I would guess that is what really wiped out your head.