The Pokemon Company and Nintendo have announced that they have plans to release a possible game-breaking bug fix in the recently released Pokemon Mystery Dungeon: Rescue Team DX for the Nintendo Switch platform. The newly discovered bug appears in dungeons with a fixed party and more details have been provided below. Hopefully this patch is pushed out soon.
Fixes a game breaking glitch that occurs in dungeons with a fixed party. It occurs when the protagonist and their partner are defeated in the dungeon, and you remove the third Pokémon from your team. To avoid the issue, simply refrain from removing that third party member. If you already have, and cannot play anymore as a result, the update will allow you to play