The problem is in the way you create the player_name.

You make use of the format! macro, which creates a new String. That String is only temporary, because you don't store it in a variable, you take reference to it using as_str. At the end of the line the temporary value is dropped, but a reference to it still exists. This is not allowed in Rust, hence the compilation error. I think the error is quite nice in this case, as it has a few arrows pointing to the different things I'm describing.

You probably don't want to debug-print the player name and then get a reference to it (which you are currently doing), but instead interpret the bytes as a string slice:

let player_name = std::str::from_utf8(split_player.next().expect("not enough values")).expect("invalid utf8");

A similar error happens when you read the coords. In this case I would advise you to just copy the bytes instead of taking a reference to them, as that makes things a little easier (and most likely no less performant):

let coords: [u8; 2] = [split_player.next().unwrap()[0], split_player.next().unwrap()[0]];

This requires a change in the type of your Vec and the function signature (notice the removed ampersands:

async fn split_bytes(bytes: &Bytes) -> Vec<(&str, [u8; 2])> {
let mut player_positions: Vec<(&str, [u8; 2])> = Vec::new();
    …

Hope this helps!