I had a similar result trying to create 16 similarly styled images. After half a dozen it just started kicking out the same image over and over again no matter what the prompt said. Even the “thinking” looked right, but the image was just a repeat. I don’t know if this is some type of context limitation or what.

I got around it by using a new prompt/context for each image. This required some rethinking about how to make them match. What I did was create a sprite sheet with the first prompt and then only replaced (edited) the second prompt.

I still got some consistency problems because there were a few important details left out of my sprite sheet. Next time I think I’ll create those individually and then attach them as context for additional prompts.