Over the past 4 weeks I've noticed that across a large number of unconnected (i.e no cross pollination of link sources) personal/client websites that I actively monitor, pages are randomly disappearing from Google for a number of hours and then re-appearing with no observable consequence to ranking position. It's not limited to the first page, I've also seen it include the second and third pages too. Is anyone else seeing this? The first 4-5 times it gave me a fright but now it's happening seemingly every other day for one ranking term or another that I check manually. The disappearances are not usually registered by rank checking software but are observable when manually checked. Just to be clear the website and the page itself remain indexed but just drop fully from their ranking position. It's possible there's some big algorithm change being split tested.