I've found that high population servers cause my character to move and slide around uncontrollably by themselves, also all functions such as opening doors or interacting with items ceases to work.
My assumption is that this is heavy de-sync at work but not sure.
Usually results in being beaten to death by zombies as cannot fight back or get into building or logout before death.
Occasionally after a minute or too it stops sliding me about but in still unable to open doors etc. And there is no de-sync message either.