Nebulous Voidcore Change?

On Tuesday I opened my Great Vault on my paladin and only had two options available, no bonus roll slot. I didn’t take anything. Today I logged back into my paladin and again only had two vault slots to choose from, but this time there was an option to take Nebulous Voidcore, which I took.

Is this a bug, or did they change it so you no longer need three vault slots unlocked to get a roll option?