Yeah, I have this issue too. I'm gonna wait a little while before trying any of these solutions because I really don't want to have to go to all of that trouble only for it to deactivate after a little while.
I love GOG and I love Galaxy 2.0 but man, they really need to get on these integrations issues.
Strange thing. Steam plugin works perfect on one of my computer (win10 laptop), but refuses to work on another (win 7 desktop). Versions of Galaxy and plugin are exactly the same on both computers. I've tried to copy plugin flolder from one pc to another, tried to reinstall galaxy on win7 pc. Nothing works. Maybe plugin devs don't support win 7 anymore ?
I'm running on 7 and most of the issues I've had with Galaxy 2.0 have either been obvious bugs or issues on my end related to all the security software I run to keep 7 alive as long as I can keep it. I refuse to willingly upgrade to Windows 10, Micro$oft can kiss my backside.