I inserted a new sensor yesterday and entered the code, no problem. The warm-up proceeded normally but the app opened up in calibration mode as if I had not entered a code. Weird! Then a message popped up that the app clock was making an adjustment (and I wish I’d taken a screen shot of that). Then the display reappeared as usual and the sensor appears to be tracking well.
FYI The calibration alerts are persistent with an alert sound that cannot be turned off. I learned this last night when I did not do the required calibration at 1 a.m.!