i found a replacement sensor from Medtronic at the top of my storage cabinet; however, it had expired in November 2019. I inserted it and waited two hours for the warm up and calibrated it at 115. Two hours later, my pump read 45 and my meter read 135. I tried to recalibrate, but of course the calibration was unaccepted.
I then removed the transmitter, recharged it and connected again. This time it only took 30 minutes before I calibrated at 130. Unfortunately, the next day my pump again declined to 40 with my meter reading 150. Obviously any calibration would be rejected so I switched over to manual mode for about six hours at which time I calibrated again with a meter reading of 130. For the next three days the meter vs Pump reading have remained close, one being identical.
I still have four days left and will see what happens.
Sometimes a little patience can get a flakey sensor to cooperate.