SMS messages not arriving on new iPad mini / iPadOS 18.1
I just received a new iPad mini Wi-Fi (A17 Pro). It updated out-of-box to iPadOS 18.1. Then I restored it from an iCloud backup of my trade-in iPad mini Wi-Fi (5th gen), which was also running 18.1 at the time of its immediate prior backup.
For reasons unknown, Messages is not receiving MMS message from my carrier, T-Mobile. The old iPad mini, and an iPad Pro Wi-Fi, and an iPhone 12, all running 18.1, are receiving the SMSes in question. The new iPad successfully makes and receives WiFi Calling calls in FaceTime. I have checked settings for both Messages and FaceTime and confirmed that they're both set to receive for the phone number in question. Rebooting and cycling the settings to receive messages at that number off, then back on, have not changed the situation. I have not yet removed the trade-in iPad from my Apple Account, but I have powered it off while investigating this issue.
Setting up all of the SMS 2FA accounts without the messages arriving on the device in question has been pretty painful; plus it would sure be nice if it worked besides. The only other consequential issue I'm having with the new iPad is an IPsec VPN connectivity issue; so it seems like the restore of settings from the old iPad was generally trouble-free.
Any suggestions would be greatly appreciated.
iPad mini, iPadOS 18