Please try the following steps in order, as they may resolve the issue.
Note:
If this error occurs only when playing the game with a specific player, that player's network environment/compatibility may be affecting this situation. Please ask the player to try the same steps as well.
1. Check for maintenance or network service outages information
Visit the official Nintendo website to see if any maintenance or network service outages are reported.
- Network Maintenance Information / Operational Status
2. If an error code appears, confirm the information for the code
Enter the error code on the Nintendo Support page "How to Find Error Code Information and Support," and try the suggested solutions.
3. Restart your devices
Power off your console and communication devices (such as the modem and router) completely, wait a few moments, then turn them back on.
If the issue persists after trying the above steps, please consider continuing with the following steps.
4. Use the network only for the Nintendo Switch whenever possible
Temporarily refrain from using other devices such as PCs or smartphones that are connected to the same network as the game console.
5. Avoid using extension cords and daisy-chaining multiple devices
Try to avoid connecting other devices to the same power outlet or power strip as your console.
6. Avoid noise and obstacles
Household appliances such as refrigerator and microwave oven, as well as other computer-related devices placed nearby, can cause communication interference.
Keep the router and the game console as close as possible and avoid placing anything that could be obstructions between them.
7. Use a wired connection
If your console is connected to the network via Wi-Fi, the connection could become unstable. If possible, please use a wired connection.
Additionally, if you are using a router, try connection without the router temporarily.