Medtronic 670G Sensor will not Calibrate

I replace my sensor each Sunday morning and all is fine until Friday evening when I try to calibrate and it will not calibrate. Last week, I tried for three hours and would not calibrate. This week, same thing. I turned off auto mode and went to manual only to be awaken all night with the alarm to calibrate. Anyone else had this issue???

I’ve experienced that issue and I usually wait until it’s ready. Call the support at MEDTRONIC they’re really helpful