The size of the "image error" placeholder is actually an issue that will exist in XF 2.1 as well.
There isn't really anything we can do about it. It's a side effect of the image proxy and the image cache size limit and allowing arbitrary sizes on the IMG BB code.
The image not loading, as I mentioned before, is expected because the image is very large and it exceeds our cache size limits.
This can be increased in your own forum as desired.
2.2 may actually help slightly as you can configure certain domains to bypass the image proxy entirely.