Nintendo has announced a downtime for Wii U online services for tonight. Players may experience connectivity issues for a couple of hours.
According to Nintendo: “From Wednesday, January 27, 2016 5:50 PM – Wednesday, January 27, 2016 7:30 PM Pacific Time” all network services may experience issues due to back-end maintenance.
Nintendo recently did maintenance for both 3DS and Wii U, but it seems the service was still not quite ready go online. Thankfully, the downtime is only a couple of hours so things will be back online soon enough.