Do you have the impression that multiple customer cards are created for each customer?
Do you have the impression that, instead of adding up, multiple customer cards are created next to each other?

If only one type of customer card has been created at the settings, it is not possible that several active customer cards are assigned to one customer. However, it is possible that there are several used customer cards and one active customer card.

You can recognize the active customer card by the blue frame around the customer card. The used customer cards have a green framework.
You can easily consult the list of loyalty cards via

1. Customers
2. Search for the customer
3. Press "Customer cards"
Now you get the list with all active and used customer cards.