Try zooming in close, then zooming back out to get Artstation to load the full resolution image.
Skybox paintings done in Photoshop for Battlefleet Gothic: Aramada 2 by developers Tindalos Interactive.
Steam page: https://store.steampowered.com/app/573100/Battlefleet_Gothic_Armada_2/
I had to reduce the quality for some of these images because of artstation's 10 MB file size limit. So please forgive the JPEG compression!