You should install the game directly to system memory in the meanwhile.
Fortnite on Nintendo Switch has been having some issues. They’re not big issues, but they’re annoying issues that nonetheless degrade the play experience for a lot of players. Essentially, there seem to be problems with how the game streams and loads buildings and other objects on the map, which has caused Epic to look into the problem with Nintendo in an attempt to resolve it.
The good news is that Epic has found what it thinks will resolve the issue, and will be targeting pushing the fix out with the 5.40 update. Until then, Epic has also announced a quick fix workaround for those who may be bothered by the problem and want an immediate redressal— apparently, installing the game to system memory over the SD card should address the issue to an appreciable degree. If you are facing this problem, Epic recommends reinstalling the game to your SD card (this won’t delete your save data).
It’s good to see them being so on the ball with this. Fortnite is available now on PS4, Xbox One, Nintendo Switch, iOS, Android, and PC.