Guardians noticed that one of the latest weekly challenges is not progressing for them and the official explanation is that it wasn't described properly in Destiny 2.
Destiny 2's new model of trying to keep players grinding menial tasks included the weekly challenges that appear in the Guardians' quest tab and require completion of various objectives. These often end up being a number of kills under specific circumstances and the challenge "Suited for Combat" that popped up in Week 9 is one of them.
The challenge requires players to score 400 points by killing anything, anywhere in any activity but they have to wear "a full armor set"[sic]. What Bungie failed to mention in the description of the challenge is that you can't just wear any armour set, it has to be Praefectus armour from the current season pass.
Yes, it's the ugly armour that no one really wants to wear and it's locked behind $10 paywall that is the season pass. In other words, it's one more of those challenges that can't be completed if you didn't buy the pass.
Luckily, this challenge doesn't reward Bright Dust so it won't be much of an issue if you are hunting for the currency in order to purchase Eververse cosmetics.
That said, it would be wise to stock up on the currency as Guardian Games are approaching soon and they will bring about a bunch of themed cosmetics that you might be interested in. Considering one set of armour ornaments costs 6,000 Bright Dust, you will probably have to spend most of what you earned so far.