Last week direct download from the website (cdn.gog.com/ ....) still worked, but for the last few days it's completely "dead". End of last year it happened already but was fine again after a few days. Hopefully it's only a temporary problem again.
It's just a bit strange that usually when something is blocked by the GFW you get a "connection reset" or "connection time-out" error. But when I try to download from GOG now, I get a "404 - File not found" error. So it can't be 100% excluded that the problem is on GOG's side. The other sections of the website (forum, library, store etc.) are working, "only" the downloads are broken.
those things come from different servers, I believe. GOG uses a CDN provider to deliver their downloads, Edgecast, if i'm not mistaken.
A little google search shows quite few news articles about China restricting access to content hosted on Edgecast last year.
As was already said above, tell the support about it.
That's right. Since the end of 2014 edgecastcdn.net is blocked in China. From then on the GOG downloader did not work anymore because it uses edgecastcdn.net as a download source. Since Galaxy does not work either, I suppose it also uses edgecastcdn.net as download source.
As for direct downloads directly from the website (cdn.gog.com/...), they were also blocked end of last year, just for a few weeks or so and after that worked fine again until last week. Now also dead. Hopefully only temporary again.
In the past I heard for such "special cases" GOG support is able to provide a FTP download option for affected users. But obviously this would only be possible if the number of cases is limited, not as a long-term solution probably.