You will see those placeholder images anytime you have HTML code that is trying to retrieve images that cannot be found. (I have already told our dev team that the text on the image needs to change, as it misleadingly implies that the issue is always on Groundspeak's side of things.)
In this case, you had bad HTML in your cache description that included a couple instances if "<img />", which is telling the server to retrieve an image without providing a source. I removed those tags and the placeholder images no longer display.
Again thank you Moun10bike for your prompt assistance.