Re: It's always DNS
Upgraded from a Livebox 2 to a Livebox Play. Got an extra half megabit on a long run of twisted pair that is older than I am and my hair is grey (I live very rural).
Randomly, my phone (S9) is unable to talk to any of the machines on the LAN using IP address. No idea why. But since the printer has WiFi Direct (which is usually faster) I've not bothered looking into it.
So it's not always DNS. Sometimes it's just shitty firmware.