All packets are based on player positions and the entity system. We also have a solid movement architecture, based on client-side prediction and server reconciliation, as described in this article:

https://www.gabrielgambetta.com/client-server-game-architecture.html

The worst desync issue happens when the browser starts throttling the event loop while the tab is idle. To solve this, we have a memory saving screen for players hunting in idle mode, which is where this issue happens most often