Expected:
Joined player will teleport to correct location and update all other clients connected to the server.
Actual:
The joined player first joins at their original location, but get teleported to the correct location on the server. However sometimes, other clients will still see the player at their original location and move relative to that.
Steps to reproduce:
1. Run a server with 2 players (local host)
2. Set a function to run the first tick a player joins (Using the scoreboard objective: minecraft.custom:minecraft.leave_game as a trigger)
3. This functions should teleport the joining player to absolute coordinates about 16 blocks away from their original location.
4. The other player can observe the joining player to be in the incorrect position.
See attached video for more details/proof.
I can't reproduce this. I've set up a repeating command block to which teleports the player as soon as they join my server, and they reliably are teleported and also visible.
A datapack added to the issue would help, as I was unsure how to replicate the described datapack in the description.