Through its official support page, Nintendo has announced that next week there will be new maintenance operations for Nintendo Network services. As you read on the site, "During the scheduled maintenance period specified below, some network services may not be available." Sign in using the Nintendo Network ID (Wii U, 3DS and Switch): From Monday 28 August 2017 to 22:00 until Tuesday 29 August2017 at 2:00 pm. We invite you to stay with us for any updates on the Nintendo world. Source: Nintendo