Hi,
A customer has been able to register three times with the same email address. I am not able to do so, so I don't understand how this happened.
The customer shows up three times in the backend under "Customers", with three different customer IDs.
Also, if relevant for the bug hunting, the customer was unable to finalise their purchase and got the error that delivery to their address was not possible (even though the country has a zone and a carrier):
There is 1 error
There are no carriers that deliver to the address you selected.
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The product selection cannot be delivered by the available carrier(s). Please amend your cart.
Their address is also three times in the backend under Customers>Addresses (btw, I think it's a bit odd that the addresses don't show up when you click on the customer's details).