GB2 isn't entirely stable yet. If you manualy move near something your should harvest, it probably will, then just stand again. Rather like its detection range is too small. People have reported some success with turning avoid ninja looting off, but ymmv. For me it worked great nabbing fel ore in hellfire penn, but over flew everythng in the borean tundra.
In a nutshell, its just flakey.
