I have gotten 3 Crux of Crotas and I have found a problem.
1) They don't stack (could be intentional)
2) You are only allowed to have 1 crux in the vault at a time, and only 1 crux in any one character's inventory at a time. So I can't put all of my Cruxes in the vault or on one character.
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Try this: make a new character, store your last crux on him/her, and you can get it with the new mobile vault feature on the app and website. Hope this helped.