Might be down to poor wording of the challenge, but it's not giving any progress toward it when killing enemies using stasis while in Vanguard Strikes. Unsure if this affects other activities - Not a PVPer, so would love someone who is to chime in on this. Wondering if it's supposed to be for guardian kills, but the wording is "Defeat targets with Void or Stastis effects. Bonus progress for killing invading guardians". Cosmic Chill is tracking correctly, hence why I'm wondering if it's an issue with wording or not.