Do a soft reset, "press and hold the power button and volume down button for about 10 seconds will do the trick; the phone should vibrate and reboot your phone."
If that doesn't work, check date on the phone.
If that still doesn't fix the issue, back up and do a full reset.
When did you first start facign thois issue? Are you an insider on fast ring? Did you do a soft reset? to do a soft reset hold volume down+lock key until phone reboots.
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