[Qwertystop]

The Switch is capable of communicating both over an existing network through a wired or wireless router, and through wireless peer-to-peer communications with other nearby Switches. Previous Pokemon games (and other games on the Nintendo 3DS) have used local wireless as a constant background feature in this manner, but to my knowledge, most Switch games that use local wireless only do it at specific times (when playing multiplayer) instead of always-on in the background, so it doesn't seem unreasonable that only the Pokemon game causes this problem, or that it would be heard by nearby devices on other networks. Other games would break it only when someone is actually playing local multi-system multiplayer Smash Bros or something, which is going to be rarer and you're probably less likely to be trying to use the Roku at the same time.

The only thing I would find implausible about breaking Rokus by proximity would be why the Rokus are picking up the communication from a Switch, when presumably they didn't break whenever someone used a 3DS within ten yards (or we'd have heard these complaints years ago). But that could easily be down to changes in protocol by Nintendo between the two systems, such that one is ignored and the other is mistaken for relevant data.

I don't have a Roku or an easy way to inspect nearby wifi packets, so I can't easily test this theory.