It's a known bug that weekly challenges pop up again. When you complete them a second time in the same week, you don't get the reward again.
English
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What the -blam!- am I even playing for then?
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Ever heard of the word "Fun"?
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I have "fun" when I level up through the time and effort I put in the game. But if the Engrams are bugged and there's nothing to gain, then I have no reason to play until it gets fixed.