Nintendo released an update for Pokken Tournament earlier today on the Wii U. The primary reason for the update was to adjust some issues with Shadow Mewtwo. Unfortunately, it seems like this patch has now created a new, and potentially greater problem.
The North American Shadow Mewtwo actually differs slightly from the rest of the world. The ‘Light Pillar’ move that’s activated in Field Phase operates differently from the other versions. As a result, the North American servers are unable to handle this conflicting data, which thus has caused NA players to be matched up with only those who are in the region.
Hopefully Nintendo/Bandai-Namco can get to the bottom of this soon.