To create a seamless loop, the best model to use is Ray2, since it offers a loop toggle option you can enable when you want your generation to loop back to the first frame. Adding the same image to the first and last frame is only a workaround, and it can still lead to issues like the error you’re experiencing.
If the result wasn’t fully compatible with your prompt instructions, we recommend submitting feedback directly by clicking the thumbs‑down icon that appears when you hover over the image. Sharing feedback there helps the team better understand the issue and improve the behavior.
Please let us know if using Ray2 resolves this issue for you.