Basically, Expedition Everest was designed to run 4 trains at once, but has been modified to run 5 since 2007-ish for higher capacity. It can do this entirely safely as it has more than enough block zones for it. However, with 5 trains, this only allows for mere seconds of delay at load or unload before the ride goes into what's known as a "cascade stop", where the ride initiates an auto ride stop from trains being unable to advance to the next block zone. Part of this is because, to avoid the trains constantly slamming to a stop right before the yeti animatronic scene, the ride system is told to hold the train at the shadow projection until the vehicle at unload advances to load. Holding the trains longer at the shadow projection is better since they are already stopped at that point anyway. This programming results in the control room operator constantly resetting these auto ride stops, as the ride control system is not capable of auto-resuming ride motion after one has been triggered. So, it's possible that this is being addressed.