It seems that not all of the entity tracker update packets are getting replaced by the network handler mixin.

"Normal" entity tracker stuff seems to be working fine until more than 1 player is online.

Sending a ClientSettingsC2SPacket (e.g. start to shift) when there are more people online, player that is disguised gets the wrong data tracker packet (it gets replaced by the data from player's disguise), leading to some strange behaviour ("icy" movement, air bubbles changing over & over again etc.)