Trying to download a new game and get almost to the end and receive this message "Connection to Communication Service has lost and could not be restored. GOG Galaxy will shut down."

I have downloaded two other games on this Mac in the past with no problem.

Hey, I got this issue when I first tried installing Galaxy 2.0 on both my desktop and laptop. I had to work with GOG support to fix it; for me, it had to do with the security software I'm running. Try whitelisting the main Galaxy directory, as well as the redists folder (should be C:\ProgramData\GOG.com\Galaxy\redists by default), in all of the security software you're running. If you need to whitelist specific files or applications, try whitelisting GalaxyClient.exe, GalaxyClientService.exe, GalaxyCommunication.exe and GalaxyUpdater.exe.

Hopefully that helps! If not, definitely hit up GOG support. They're pretty much the best support team in gaming, at least in my experience. Usually quick responses, friendly staff and they know what they're doing.

EDIT: Sorry, I missed the part where you mentioned you're on a Mac. I'm not sure how MacOS works but maybe the suggestion above can help you figure out a solution? If not, definitely submit a request to GOG support.