FALSE ALARM. As you can see below the old stickers are back to normal and don't show up blank. Sorry to cause all this ruckus for nothing. But really, affiliate images have been pretty funky lately. I've seen ones upside down, and in half, etc. Very strange.
Zazzle has updated their images for stickers. If you have linked to any stickers using the old Zazzle code, they may come up totally blank, like the ones below. I've seen this on neckties too...which recently changed over to a new design.
You will need to grab new code for all your stickers. New stickers will look like this (well, you know...only with your designs)....