But all those links/folders on http://snapshots.packages.x2go.org/ seem to be empty.
Or am I missing something?
Nope, they are not. See for instance https://snapshots.packages.x2go.org/20180302/fedora/27/main/x86_64/rpms/nx-l...
It's just the index page that is "blank", just like https://packages.x2go.org/ is.
Fixing the bug could take weeks, so it would be good to roll back 1 version that seemed to be more stable while we wait.
The other version has a different severe bug, related to Screen Savers and DPMS. Make sure to disable them, if you really want to downgrade.
Mihai