3DS keeps disconnecting from the internet.

I've had my 3DS for almost a year and I've never had problems with this until recently. It connects to the internet no problem, but after about a minute it disconnects and won't reconnect again for a while. It's been doing this for the past couple days and I don't know why. I don't think it's because of unstable/slow internet either because I've been using the internet just fine on everything else and I've used far worse internet on my 3DS before with no problem either.

I had a similar problem, I reset / restarted my router / modem and it fixed the connection problem immediately

That didn't work. I know it's not a problem with my 3DS either since I just set up another 3DS next to mine and they both disconnected at exactly the same time and couldn't reconnect for a while.

Apparently my Wii U has started doing the exact same fucking thing.