I have already tried to do everything the GOG technical support told me, but nothing worked. Looking at the logs, I consistently get this error:
[HttpClient] Request failed with CURL result 35, curlResultStr 'SSL connect error', address

I have Windows 8.1 32-bit and I can't get cloud sync to work for Legacy of Kain Defiance.

Make sure the LSASS.EXE Windows service can access the Internet.
https://www.gog.com/forum/general_beta_gog_galaxy_2.0/cloud_sync_failed_for_all_installed_games/post5