Hi there,
When I enter a new address in the customer center and then reload the page, the address gets added again. It looks like the module directly returns the list view content after an add and does not redirect to the list view. That means that the form data is still in the request and a reload will resubmit it causing the duplicates.
I can repro this in Rapido 3.4.2 and in Swift. In the latter case, you're asked if you want to resubmit which at least mitigates the issue somewhat; in the case of Rapido it just silently resubmits the form and duplicates the address.
Happy to provide more information if needed.
Imar