spark plug failure

Running NGK BR8EIX plugs on my IO-320, two p-mags. Run up pre flight, L mag test, bad miss, number two cylinder EGT drops to 700 degrees.
Darn!
Taxi back, pull the cowlings and see nothing wrong. Pull the plugs, a little rich but not too bad. Check all the plug wires, find nothing. Run it up again without the cowling on, number two cylinder drops EGT when on Left mag.
Pull the plugs again and swap with number one cylinder --- this now becomes the cold EGT with left mag.
Ahah moment. Spark plug is bad, resistance is infinite! No marks, cracks or discoloration on plug. Go down to local NAPA and replace the plug and all is well.
I have never seen this failure on and auto plug before. Has anyone else seen it?
Thanks

How much time did you have on the bad plug?

With the EICommander, we have seen plugs go bad at around 100 hours. That's why I recommend our customers run the BR8ES plugs and just replace them every year.

Under ten hours on the plug. Assume just defective.