When connecting to a server that has server-authoritative-movement set to client-auth, if you move, your movement is not replicated on the server, resulting in your true position never changing.

You can verify this by doing the following:

1. Have some items in your inventory
2. Walk some blocks away from where you spawned when you connected
3. Drop the items
4. Observe the position where the items are dropped: where you spawned when you connected, not the camera position.