My wife's Note 5 says that the SIM card is not detected and to restart. This happens all day long. She just had her SIM card changed because of this issue at AT&T.
I guess that didn't fix the issue. Any suggestions on how to fix this?
Eject the tray and use a can of compressed air to blow out the SIM slot. If that doesn't help, see if the problem persists in Safe Mode: https://support.t-mobile.com/docs/DOC-27639