Make sure you’re checking mash pH about 10-15 minutes in, not after the mash. The pH will continue to fall a bit throughout the mash.
Also, don’t stick your pH meter into something so hot!!!!!! You’ll ruin the electrode. Measurements are always done at room temperature. ALWAYS. Even if you have ATC, it won’t protect your meter from those high temperatures. ATC means that the meter will adjust to temperatures variations in the sample, say like from 68F to 72F, not that you should stick the probe into hot samples!
Cool your sample. I use a shot glass to hold the mash liquid. Cool that in a little ice water bath too under 80 degrees. THEN take the pH. Make sure you don’t have any grain in the sample.