After downloading an update to my S7 on March 1, 2019 the SIM card stopped working. I have received multiple errors. I've done multiple hard resets to the phone. It will connect to the Sprint LTE Network and then the Samsung DM Service will say "Checking device status...". After a couple of minutes I will receive the following message:
"The SIM card has locked. Please power cycle the device and if the problem persists contact Customer Service"
Then the phone will say Invalid SIM card.
Two major things I also noticed. My network now says T-Mobile under SIM card status. I have never changed my SIM card.
That's weird, but not unheard of. You are a Sprint customer, correct? Is the phone a BYOD that originated from T-Mobile?
Intriguing. I'm going to send you a private message to get some information from the phone.