Probably a little bit late but I will reply anyway.
The general issue is caused by IPV6 not being enabled by your ISP at the premises your DVR is located.
A quick fix for this is to download an app called 1.1.1.1 which is essentially an free VPN.
Download the app, turn on warp and you should be good to go on 4G network. I am however aware that the latest IPhone update has messed a lot of things up again. So if you have not done the latest update, DON'T.
Or you could just call your ISP and ask them to activate IPV6 on your modem
