During the Splatoon 1/Wii U era, my ISP changed some settings that blocked Nintendo online play specifically (including 3DS games) and only at my home area. I couldn't play for a couple of months (no Splatoon, no Smash, no Mario Kart, etc.) We had the same ISP plan at work and my consoles worked/played fine there.
I actually had to contact Nintendo to ask for some network data that my ISP needed to investigate what was the issue. It was a lot of back-and-forth. In the end, they had to "reroute" my area network to another node in a different state or something along those lines. I remember they actually sent several tech guys to check if everything was OK on my end, one of them told how once they changed some configuration and Call of Duty became unplayable (lots of angry gamers called
).