The command ctrl+/ or crtl+shift+/ doesn't work.
I have Ubuntu 13.04 + Gnome-Shell and ST3 Build 3033 I've no extra plugins or syntax higlights
With ST2 that I have the regular license the comment features works well.
Yeah! I have the same problem and configuration
for me worked this solution
from the thread: https://forum.sublimetext.com/t/st3-3012-toggle-comments-broken/8930/8