The well page used to show the same empty state whether an image was still being generated, had failed to load, or would never exist — and it started an expensive in-browser stitch in all three cases. It now names which situation you're in, so a brief wait is distinguishable from a genuine problem.
The page also holds off on the in-browser stitch while a server-generated image is about to arrive, and only falls back to stitching once it knows that image isn't coming. "Well image unavailable" now means every fallback has been exhausted, not merely that one source was missing.
