We're experiencing this error when fetching images. I've checked if the server(smush7.wpmudev.com) has been blocked in any way at a hosting level.
We use iThemes Security, I've disabled that and tried to retrieve again with no success. We're currently not using any caching such as W3TC et al, but use Autoptimize, which hasn't blocked this previously.
Not sure what's going on, any assistance would be greatly appreciated.