[url=https://gameranx.com/features/id/187201/article/pokemon-sword-shield-disable-autosaves-to-avoid-this-sd-card-corrupting-bug/]Gameranx.com[/url] said:
Before beginning your adventure in the new Galar Region, you'd better take some precautions to avoid a game-breaking bug that's completely corrupting files in Pokémon Sword & Shield. The problem, reported by many players on Twitter and other sources, is related to the auto-save function. If you have downloaded games on you SD card, you might have to redownload them if this bug happens to you — which is incredibly annoying.
Basically, the best way to avoid this problem is to disable autosaves and only save manually. This also seems to only be occurring with the downloadable eShop version of Pokémon Sword & Shield — it's the version most players are able to get a few hours earlier. The bug occurs when the game crashes when attempting to autosave. After the crash, you'll be unable to access files on your SD card.
The Switch system will force you to reformat your SD card to make it usable again. Save files aren't stored on the SD card, but everything else will be lost — video, screenshots, and games you've downloaded or installed will be deleted in the reformat. It's incredibly annoying, and one of the worst Switch bugs I've heard about in recent memory.
Here's hoping Nintendo will step in and fix this bug fast. If you don't have online enabled, it might be a good idea to connect so you can download any patches coming down the pipe in the next few hours / days. Corrupting files is a pretty bad look.