Updates

For some reason I can not update two out of four iPad Pro 12.9” 3rd gen. I have tried different WiFi networks, vpn’s, restore, restore and update on MacBook. One is trying to update from iOS 12.something and the other is trying to update from iPadOS 13.1. One of them I was able to update by hot spotting to my phone, but the last two will not work with that method. Is anyone else experiencing this? Is this an apple issue or a hardware issue? Please help.