Duplicate Payment Items

The back button problem seems to happen quite often, at least at the website, we have added Klarna a few weeks ago

Happened again... quite every day now.. one thing, I missed out to add: we never have a second payment entity, but checkout complete event is triggered twice, which triggers the order place transition twice, and any event subscriber will trigger twice. So the customer will receive 2 e-mails with two different order numbers, etc

Added 📌 Controllers handling order data should use loadForUpdate() Active and ✨ Klarna Payments Authorization Callback Active as related issues, as both should improve/solve this problem