I've just tried this, after updating the Downloader and found it was crashing; it seems to download the main installer and the bonuses with no problems, but when I've clicked on the "Universal update, english" it kills Downloader, I've tried this on "Forgotten Realms: Demon Stone" and " Legend of Grimrock" so far. If you want me to copy the log entry, I'll make it crash again, though I'm not 100% sure where I need to copy from/to.
I've checked your issue, and from my side (home PC) it works fine. Are you sure you are using the new GOG website? We pushed small update today. Please copy and paste me the links which are crashing the GOG Downloader.
Just to clarify, I cleared my Cookies and Cache in the browser, reopened GOG.com and then did CTRL+F5. When I look at "Forgotten Realms: Demon Stone", these are the download links showing up:
For "Legend of Grimrock":
ETA: I meant to say, the last link, each time, is the one causing Downloader to crash. I haven't tried any other games, yet, so if it is just these two then it's one heck of a coincidence that I happened to try just these.