I was able to fix but I'm not sure of the technical aspects behind it. I changed security settings on the T-Mobile router from WPA2/3 (default?) to WPA (no trailing digits). This meant my older iPad devices were able to connect. I don't know the security ramifications of this, in case someone cares to explain.
Already have an account? Login
Enter your username or e-mail address. We'll send you an e-mail with instructions to reset your password.
Sorry, we're still checking this file's contents to make sure it's safe to download. Please try again in a few minutes.
Sorry, our virus scanner detected that this file isn't safe to download.