Now I have seen a problem where 4G apparently disappears for no reason. It shows no 4G/3G and it really does have a problem because if your disable Wi-Fi to force it to rely on 4G when in this bad state it fails to access the internet with browser err msg for example but the coverage is fine and an o/s restart fixes the bug
Ios13 is really really bad news and should be avoided by everyone - iPad Pro v1 with 4G NIC built-in ; iOS 13.1.3