One of my companies costumers experience that on some of their site collections, the Quick Launch will randomly miss a few items once in a while. By iisreseting they will get restored, but that does not solve the problem, as it keeps occuring that items will disappear.
The costumer has SharePoint 2010 solution. We have no publishing features activated and the SharePoint log doesn't give us any kind of details towards why it happens.
We have experienced that this occurs after we deploy or update the costumers solution, but then we're back at the iisreset, which again leaves us as big questions marks as it still happens all random without the deploy or update to trigger it.