Some agreed this is not caused by Nintendo.Reddit community agreed this may be a bug.The same basic kind of 'anonymous guest' can't sensibly be used.' Each player's characters are stored in that player's profile / saves. /u/Robin64 - 'It's completely different because the other players aren't making use of distinct local profiles with their own progression and such stored completely separately.

Mario Kart co-op online doesn't use two profiles.More gists (correction for the strikethrough text): The author did specify a player can make seasonal characters with or without Switch Online, but it requires Switch Online to actually play online.The author has tried both using a normal character and a seasonal character.If declined linking it, it won't work for online. When choosing that account as the 2nd player for Diablo online, the game forces the author to link it to a Nintendo account (presumably to check for online subscription). The author made a new guest account and didn't tie it to an account.The author said it doesn't matter if the 2nd player's account/profile was tied to another Nintendo account.The author tried out the same thing with Mario Kart 8 Deluxe, and noted that 'you can play 2 player on 1 switch online, with just 1 online subscription.' But, this has been pointed out that this is offline local multiplayer, which is allowed.However, the author attempted to play locally with a 2nd player (on 1 switch), and found out the game is unable to go online with that 'user account', as it doesnt have online access.The author has read about the game that it would require the Nintendo Online Subscription to play online.

Diablo 3 switch gameplay couch co op