I also have 2 active DCs.Just checked again on her account, its not showing 2 active cards anymore.
What had happened around 8 months ago:
Its wealth account. The original DC issued was wealth on MC network. Thought that if we ask for Visa then would get the Wealth select which looks great. But what came was a Visa Platinum without word wealth written on it. So again ordered back MC.
Probably one of the later card was not activated, so kept showing in the account for a long time.
Wealth management world debit card ( MasterCard)
Private banking ( Visa Infinite)
I use both whenever needed.