Damn this game is a doozie. I got a response from support, and as expected it's the ''make sure your firewall isn't blocking Galaxy' stuff like with Bioshock. Well, I've added Galaxy's processes and the game to the exceptions, tried running it without a firewall, even uninstalled Norton just to make sure it's not the cause. No dice. Now they're asking me to make sure that GOG.com domains are whitelisted. Any idea how to do that? Though given that no other game has consistently failed to reward achievements, I don't think this is where the problem lies. Other than that, all I can thing of is to redownload/reinstall the whole thing, try it on my old laptop, and try someone else's save file. And yeah, the same achievements seem to be working for others, they don't seem bugged globally.
Edit: It's done, Support have thrown their hands in the air, as have I. I'm getting a refund. Might seem petty to refund a game because of achievements but the complete disregard from the devs in their own tech support thread (and not just towards me) makes it easy to get over.
I'm very sorry that you couldn't solve the problem, unfortunately I couldn't have advised you anyway because I have no idea what else could have been done. From what I understand the developers have been bankrupt or are very close, so maybe that's why their technical support leaves much to be desired.
In Darksiders Genesis the achievement for defeating Belial appears to be broken. Based on the screenshot I've attached there appear to be a few other broken secret achievements as well; all boss fight related.
A developer told me to send a ticket to this link (click on the + at the top left). If you have the chance, I guess the more tickets the better: https://redmine.thqnordic.com/projects/darksiders-genesis-community
Achievements for Apocalipsis: Wormwood Edition have partially stopped working. I have tried multiple times to unlock "Magic", but it doesn't work. Unlock rate is considerably lower than on Steam. This is also the case for quite a few of the other achievements. The first achievement from the DLC "Goodnight" does work though. I haven't tested any of the other achievements yet.
Strange, I played it not so long ago and I unlocked all the achievements without any bugs. I'll have to investigate if in the meantime it has received updates.