Nintendo has a maintenance scheduled for the Nintendo 3DS during the middle of the week. There is nothing planned for the Nintendo Switch at the moment.
During the maintenance window, all network services will be unavailable. Online play, rankings and other activities that requiere the use of an internet connection will stop working during maintenance times.
Here is the schedule:
Nintendo 3DS online play of some software
- From Tuesday, November 24, 2020 5:00 PM to 7:00 PM Pacific Time (PT).
- From Tuesday, November 24, 2020 8:00 PM to 10:00 PM Eastern Time (ET).
- From Wednesday, November 25, 2020 1:00 AM to 3:00 AM Greenwich Mean Time (GMT).
- From Wednesday, November 25, 2020 2:00 AM to 4:00 AM Central European Time (CET).