Hoping this will jog someone's memory.
There's an issue which occurs on some high traffic servers where clients with higher latency will lose sync once they zone in. The client still receives certain updates, such as player location info, but most packets are either no longer sent by the server, or aren't received by the client. The issue only occurs in zones which have a high number of updates to the MOB list (e.g. Hub zones, or public zones where a LOT of mobs are spawning and dying). Anecdotally it occurs more frequently when a zone has been up for a long time, but a couple of times I've also seen it occur shortly after a reboot.
I spoke with someone about it when THF ran a halloween event in the Karana's but can't recall who it was.. so hoping this will jog their memory. We talked about pointers and the Mob list.. send me a PM if you remember
If anyone else knows more about the problem would love to hear from you as well. From conversations I've had with others I believe this issue has been seen on some of the other large servers as well.