The missing pages are also back, including
Risky's Revenge which is earlier in the series (but has some technical issues it sounds like). I'm no expert but I guess the giveaway would be something that can't be done by the CDN so I'd guess the issue was GOG's own servers getting hammered somehow, either a configuration issue or an attack (I'd guess some of the haters don't just write nasty forum posts) or both.(*) The insomnia sale was gone for a bit, possibly the issue was related to that somehow (edit: nevermind, it just seems to disappear if I leave the page for a while). Thanks GOG and Wayforward for the giveaway and the web team for getting things working again :). The new insomnia design looks nice too.
* If that doesn't make sense to you, my attempt at a basic explanation: Most websites these days have essentially two parts, the Content Distribution Network, a service provided by a few large companies that locate pages that don't change around the world to be as close as possible to everyone viewing the page, and the main servers run by the company whose website it is. These main servers have only a tiny fraction of the capacity of the CDN servers and various configuration issues or other unexpected situations can sometimes cause the CDN to send requests to the main servers that should be cached and this can overwhelm them. The main servers then ideally drop connections when overwhelmed; the extra traffic can cause a massive unexpected hosting bill, particularly if it autoscales to try to handle everything. Because this situation can either make a website not work or cause a massive unexpected bill or both it is something that people trying to attack a website look for and even obscure configuration issues that would never normally cause trouble can be exploited.