iPad Pro 9.7 w/ cellular won't activate after removing Verizon SIM card from sim tray

iPad Pro 9.7 w/ cellular won't activate after removing Verizon SIM card from sim tray. (Deactivated cellular to use only Wi-Fi ). I've restarted it, reset network settings, and also tried activating with iTunes and using AppleID. This issue occurs when the SIM card is not in the sim tray. Goes away when I put the SIM card back in the tray. I finally erased IPad and recovered from ICloud backup. Still unable to remove Verizon SIM card from tray without message appearing that iPad is not activated. Apple advised to have Verizon unlock the SIM card. Verizon swears it was never locked. Have tried both with a Verizon SIM card from another IPad and current SIM card. It works normally with either SIM card in the tray and not without. Is this a hardware problem unique to the IPad Pro 9.7 ? Verizon says removing the SIM card should not trigger activation issues.