I think the huge reduction in ANC you experimented is somehow related to seal test failing.
Keep the post update after the swapping. I’m curious to know if they’ll give you a white box replacement or new product...
Yesterday I got my replacement pair. It was a white box replacement. It wasn’t exactly a positive experience with the Genius Bar guy. When I got home I could see and feel residual glue on the seems of the left airpod. The seem also looked dirty. Maybe just bad luck. Or maybe a previous returned one. idk.
I returned them today. Got a full refund, also full refund on AppleCare+. I feel relieved.