there is an occasional network desync issue on fresh spawn, where if the player doesn't wait a while (not sure how long, although it seems to depend on server performance and the player's connection quality - but say, 20-30 seconds), when they start moving around, there's a chance the server thinks the player is holding a particular movement key while the player isn't actually holding a movement key, and on their screen they will see their character 'teleporting' in a laggy manner in whatever direction the server thinks they are supposed to be moving.

the player can normally solve this by pressing each movement key long enough to 're-sync' with the server the state of their movement keys.