I have the shadow mundus stone and the fighting finesse cp perk active, and yet the value stays at 0%. Not sure if other stats are bugged in a similar way or not
It was just UI on the PTS. It was broken since 6.3.0 hit the PTS and was never fixed. Both crit damage active stars and the Shadow worked as of last PTS patch, but better test to be sure.
The Advanced Stats number is stuck at 0% even if you have a class or racial passive that adds crit damage.
Still an issue in High Isle. Crit damage stay at the base 50% and only the Shadow mundus is actually having an effect on the displayed number in advanced stats.