There was a bug that if you didn't open a treasure from the previous week before Tuesday reset; then you would not be able to earn that treasure the next week. This was fixed in the 4/20 hotfix, but is probably what hit you here.
Sidenote, the 15 marks for the daily appear to be rewarded for completing the heroic weekly story missions as well (20 + 15 = 35). They don't have to be coincidentally the same mission either.
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Possible, but I generally open the chests as soon as I get them so I don't think that's it. It's NBD, but it seemed like a possible bug in the interaction between the first weekly clear and if it happened to be the daily mission so I wanted to see if anyone else had run into it.