Check your rewards tab. Iirc new expansions go there and don't always pop up properly while old expansions put a thing in your inventory.
Odd, I had no problem using the Overseer Collection Item Dispenser to get around 50 CoV collections and finish them off (I was a slacker this last expac).
Ah, you're right...I misread it. There were some issues with CoV not showing up as a reward when you had a critical success on research tasks. Maybe the same thing is happening here.
The overseer quests give dispenser fragments, not a collectible reward directly, so it wouldn't be an issue.
Any chance of a screenshot of what you're seeing? I collected dozens of shinies from CoV via dispensers across 3 accounts and didn't have an issue. It may seem like a silly question, but you do have CoV enabled on the account, yes?
