Me too, OP.
I ended up just feeding the birds and squirrels and I'm pissed, I just wasted $30 worth of grain. I have three....I repeat three thermometers and all of them decided to act up.
I heated up my water, pre-warmed the cooler, got the strike water to 170 which was a tad hotter than I needed, added 3 gal of water... added grains...mixed took temp.... 163. Added cold water (half a gal)temp dropped to 148, added more hot water and and it just continued on from there.
I dumped it on the grass I was sitting at 144 with almost 7 gals in my mash for a 5 gal batch. I would have nothing for sparge if I continued. The thermometers, one read 144, on read 136 and the other read 140. I kinda trust the 144. And I mixed the living hell outta my mash.
My first complete failed brew.