[@: Can only manipulate existing players]
I have added a player, and then I kill it, and then It log out and the console is like this
[@: Can only manipulate existing players]
[@: Can only manipulate existing players]
[@: Can only manipulate existing players]
[@: Can only manipulate existing players][@: Can only manipulate existing players]

That looks like there's a command block or something (datapack, scarpet app?) trying to use the removed player.

And if I add it in, it become good

I mean the player

Closing this as it shouldn't be an issue with Carpet and there's been no response for a few days.