After installing the new patch, I was having problems with free DLCs too. On top of that, GOG Galaxy started downloading the patch all over again! Fortunately I fixed this issue by uninstalling then reinstalling GOG Galaxy and importing my game folder. It verified the game folder for me (took about 30 minutes to do so) and is now working as it should. I hope this helps.
While verifying, it'll show up as downloading in the GOG Galaxy but it won't be downloading any new files. It does use the internet but just to verify existing game files on your HDD.
Post edited October 12, 2015 by ScarletCrimson