I encountered this exact problem last night with my Z9 and brand new Lexar Gold 1TB, also in slot 1. The matching 1TB card in slot 2 releases fine. I haven't tried the fridge/freezer method, but otherwise I have not found a solution for this yet. This was the first time I used this camera for a shoot, and didn't even shoot the volume or pace where the card would have expanded at all from heat. I did a couple of test shots when I first got the camera, with a 512GB Lexar card, and that released fine in slot 1.