If they have 'disappeared' from view when in the hub's edit mode, I'm not sure. But, if they have 'disappeared' from view on the screen once published, I have noticed that the last few days. It seems to be a problem with loading an window from the internet. I'm thinking it is a problem with capacity, either with the server or elsewhere that the server administrator must be working on to increase some how. May be a high traffic season with Memorial Day shoppers heavily surfing for deals, is my guess.