Hi,
I've seen some other reports of the same issue for over 3 years now, but this is still happening:
Connection to Communication Service was lost and could not be restored! GOG Galaxy will now shutdown.

Everything was working perfectly, until 2-3 hours ago when the error suddenly appeared and it's not going away, force closes GOG after 2-10 seconds of its launch.

Please kindly note:
1. I am not using Remote Desktop/RDP etc (I've installed GOG on my Macbook)
2. I have tried restarting and removing GOG and all (~/library) files of it before installing it again, but the issue persists.

P.S. I'm using GOG Galaxy Version 2.0.41 (110) on macOS 11.5.2

Okay, after working on this for ~4 hours, I finally managed to get it working on my Macbook!

Here are the steps I did:

1. Download "AppCleaner" (free) and delete GOG Galaxy with it (check to delete all files)
2. Go to "~/Library/Application Support" (using Command + G) and delete GOG.com folder inside
3. Go to "/Users/Shared/" and delete GOG.com folder there
4. Restart
5. Install GOG Galaxy again

I believe this is a long-known bug with GOG Galaxy and should be addressed by the devs.

I keep having the same issue (on Windows). I've uninstalled rebooted PC, deleted all files in Program Files, Program Data and AppData folders which should fully reset. Then installed again.

I am still having these issues. It mostly seems fine during the day but evenings are really bad where I get the message after around 10-30 seconds. Impossible to do anything with it. I have raised a ticket myself with Support. I will see what they say.