trancelr: I faced the same issue and tried to add firewall exceptions for GalaxyClient.exe and GalaxyClientService.exe (I don't see the point since normally, Windows prompts automatically to allow or block when a port opening is requested for the first time) but problem persisted.

I tried to launch these commands in an admin prompt :
net stop winnat
net start winnat

Then I can launch Gog Galaxy, wait few minutes without the "Communication Service was lost" message.
No need to disable hyper-v or reboot Windows.

Too bad I didn't try first this command first before restarting winnat service :
netsh interface ipv4 show excludedportrange protocol=tcp
to check if some ports where locked

It looks very similar to this problem with other softwares (like IntelliJ) from JetBrains company that made me think to try this winnat restart solution when seeing some people's posts about hyper v deactivation to solve the issue : IDEA-238995 (links are blocked right now...)

Too bad the gog galaxy message is too generic enough "Communication Service was lost" and not accurate enough like port <port number> is already used or something like that can help to better understand the root cause and google it for a solution.

freakyweasel: Alright, this worked for me:

Press WIN + R

Run: services.msc

Then locate GalaxyClientService and GalaxyCommunication

Double click each, then change Startup type to "Automatic" for each one, then select OK.
Hope it works for you, too.

ppmartin: [Amended] Unfortunately, this solution didn't stick, and the problem game back after a short while.

ARCADDER: Yesterday I came back to GOG after maybe 5 years of not touching it with the intention of finally ditch Steam. I purchased $60 worth of games. I turn off my PC, and today I can't even open the launcher because of this stupid error.

If I knew this was going to happen, I wouldn't have bothered with this storefront in the first place.

ARCADDER: Yesterday I came back to GOG after maybe 5 years of not touching it with the intention of finally ditch Steam. I purchased $60 worth of games. I turn off my PC, and today I can't even open the launcher because of this stupid error.

If I knew this was going to happen, I wouldn't have bothered with this storefront in the first place.

igazine: it's crazy how nobody gives a crap about this issue. seriously i have 384 games bought and can't play any of them because of this long going issue.

FrodoBaggins: Um... what do you mean, you're unable to use your account anymore?
You don't need the galaxy client to access your account.
Just download your games normally, form your account here - https://www.gog.com/account

eglinski: This just downloads a GOG Galaxy client, which no longer works for me either. Same error.

RikuRecon: I'm unsure if this will help anyone out but I'm on Mac OS and I just got this error after installing GOG Galaxy. It worked fine for a while but then it didn't lol.

I tried the majority of the solutions here but they didn't seem to work Here is what DID manage to fix my install, however, and get it working.

1. Delete the current installation.
2. Re-install GOG Galaxy
3. Add GOG Galaxy to my On Startup apps. You can do this by searching for "Users and Groups" in Spotlight Search (CMD + Spacebar), going to the Login Items section, opening the lock to make changes, and clicking the + button to add an item. Add the GOG Galaxy app from the popup window. Close the lock to save.
4. Restart your Mac.

Seems to work now and I can install games. My stats for my games is completely different though lol.

Edit: similar steps for Windows might help? Unsure if it will since I don't have one