Okay, maybe not that simple. The problem was back after a while. I noticed that the problem images were > 600K, so I resized them to 200K, and it seems to be working okay now (knock on wood).
Also, I tried it in another browser (Opera as opposed to Firefox, to see if it was a browser problem), and strangely, Opera just skipped over that photographer and loaded images from the other photographers. Funny that different browsers should treat that problem differently.
So if your Random Gallery Image sidebar seems to be skipping certain images, it may be that the original images are too big.
