Ad images vanish

I have been using a patched 4.6 banner module for a few months on http://nicaliving.com with pretty much success. A week ago, the image for one of my ads (there are four) vanished. So, I uploaded it again. Today, the image for another ad vanished.

I have no clues here as there is just too much traffic to find much interesting. So, I am mostly putting this out there as a "did this happen to you"? If not, I will assume it is the phase of the moon or something. Otherwise, let's see if we can invent an organized attack to figure this out.