I have an iPhone 7+ (NN4P2ZD/A) that has been having weird issues with connections which I’m attributing to DNS resolution problems. They only occur on home WiFi network and they only occur on this one device.
Often trying to browse with Safari I get “cannot fine server” issues. Applications load some images but not others (assuming they have several servers for them so some resolve, some not). Discord, for example, can’t send photos but messages go through.
If I drop out of WiFi to 4G all works. If I start a VPN connection everything works. If I connect to another WiFi network somewhere everything works. And after that the cached information makes all work on home WiFi until it later on breaks again (assuming removed from cache). If I change DNS manually to something else than my router it sometimes helps a bit, but doesn’t entirely fix the problem.
Note that this isn’t all addresses, and as I said, all other devices in the same network work. iPad 2, iPad Pro, laptops, Android devices, iPhone 5S... No issues. This device has had it always and with different iOS versions (currently on latest). There’s no clear connection between the addresses that won’t work, but Discord is one that often breaks. Twitter also often won’t load properly.
So far I haven’t tried to dump all network data to see what’s happening but I really can’t figure out what could be the issue.