Static devices (as opposed to DHCP reservations) will just (seemingly) randomly stop working with port forwarding, as the router just forgets the device. You can shake it out of that by pinging the device from the router's diag tools, or power cycling the router resolves the issue. Not great for CCTV DVRs/NVRs.
"Smart setup" sometimes breaks stuff, especially IoT stuff.
Your device may or may not just randomly factory reset itself. (I've had one do it twice in three years, to the point where I now save the config.)
It may or may not completely ruin your Sky Q system's reliability if you have more than one box (although I generally advocate wiring them in completely and disabling all wireless functionality anyway).
The automatic channel setting for the WiFi channels is a total dice roll.
The DNS interception rubbish breaks stuff. Most recent example was I was having infuriating issues with Ubiquiti's AP guest portal... Until I switched the BT Business Hub into a dumb modem and put a cheap ER-x in front. Rock solid since.
He was paying €15/mo for 4K television plus 1/0.6Gbit fiber internet on custom hardware they'd provided. I can't help but feel something went terribly wrong in the US for us to be happy with our $80/mo cable options and dated, generic hardware.
and what exactly could I be doing to cause random DNS failures, or to cause DHCP to fail only on Ethernet ports? these things can't be configured to do that. they're consumer-grade routers and consumer-grade routers are garbage. all of them.
every enterprise router or access point I administer at work functions just fine for years at a time.