About a week ago, Nintendo launched the Version 2.0.0 update for Super Smash Bros. Ultimate, adding Piranha Plant as a new fighter. Unfortunately, it seems that patch may have also added in some bugs, as players began reporting save data corruption under certain circumstances. Nintendo was silent on the issue for days, but now they've finally chimed in.
Some players reported that playing through All-Star Mode as Piranha Plant destroyed their save data, while others encountered a similar problem triggered by playing Century Smash as Duck Hunt or Mii Swor,dfighter. Here's what Nintendo has to say about the whole matter.
"We are aware that some users are posting about possible issues with the latest Super Smash Bros. Ultimate update. After extensive testing, Nintendo has not been able to confirm that there is an issue, although we will continue to investigate and monitor the situation." — Nintendo
It's certainly not great news that Nintendo can't seem to find the problem, especially for those with corrupted save data. However, they seem committed to a continued effort here, so hopefully it's just a matter of time. Until then, we'd advise you to be cautious about the characters and modes you play to avoid the possible loss of data.