I tried to install Invisible Inc, SuperHot, and Undertale. The latter two failed. I checked ProgramData\Gog.com\Galaxy\Logs\GalaxyClientService.log and I see quite a few of these:

Couldn't create process as user due to elevation issues

I checked that the two Windows services related to the GOG client are both set to run as Local System.

Any ideas how I can fix this?

The games seem to have installed -- I can browse to their local folders and run the executables. Running repair didn't fix the problem, either.

It might be necessary to drop the PC in an ocean. It seems to be having issues with your altitude.

This. I was going to suggest moving closer to sea level. Ashes, you don't live in the mountains, do you?

I don't understand. They failed to install but they installed? Which is it? Are you sure you're not misinterpreting something in the log?

That would explain why nobody in Denver buys games here.

Correct -- they failed to install but they installed. The UI lists both games as "Installation Failed" but the binaries are on the file system, and the games are runnable. The UI doesn't let me play the games, though, because installation wasn't complete.

The log files report several issues with elevated permissions. I did, but not on the Windows/system drive, on a data drive. I'll uninstall and reinstall, or see if I can move my games so I don't have to re-download everything.

Thanks, I think this is probably the actual root cause of the problem. I was able to move the games folder, re-import into GOG, and now the games show up as "installed."