This is all I've been getting since yesterday afternoon. I'll hop into a lobby, other users will pop up, if I'm lucky I'll connect and have a match for about a minute before it says "connection unstable" and I get booted out. I've been able to play 2 games all the way through between yesterday and today. Tried using Netflix on the Wii U, and it streamed perfectly for an episode and a half before I chose to exit out of it.
Already tried expanding my ports and putting the Wii U into DMZ mode as well as restarting the router. It's really frustrating to not be able to find a concrete solution regarding this. Every thread I've found of people posting of their issue have a billion possible solutions offered up and half the time end in "well, either [x] solution worked or it just kinda fixed itself on its own."
I'd played this game without any connection issues for the last week and a half and now all I get is this (despite not changing anything on my internet settings beforehand). Super annoying.