Whenever I try to install the game via Galaxy my antivirus (using the latest version of Avast) goes bonkers and is bringing up one alert after another (as in like 50+ within 20 seconds). Now this is olny happening when I try to install Darkest Dungeon. Any other game I can play and install just fine (just tried it with OlliOlli2). Hope you can help me with this.

Edit: Problem solved itself.

Bumping this because I'm experiencing the same issue with the Avira antivirus. From what I can tell, the AV is actually preventing Galaxy from finishing the download.
I'll try whitelisting the partial download, then I'll do a full scan of the game directory and edit this post with the results. Hopefully everything will be clean.

How exactly did the problem "solve itself" for you? Did you manage to complete the installation without any further action on your part?

EDIT - The game directory is clean according to my Avira installation. It may very well be a false positive after all :V