On December 21, 2018 a new software update for Super Smash Bros. Ultimate became available for download. Please take a moment to download and install this update while your Nintendo Switch console is connected to the Internet.
- Various fixes to improve gameplay.
- This update must be applied in order to use the game’s Internet features.
- All players must be using the same version of the software to participate in Local Wireless Battles.
- Replay data from previous versions is not compatible with the newest version. Be sure to convert your replays by going to Vault in the main menu and selecting “Convert to Video” before updating the software.
- Save data will still be available for use after downloading the update.
- If the system is connected to the Internet, the update will download and install automatically.
Source: Nintendo Support