Rival eTap AXS Chain Sag

Hi,

My Rival eTap AXS chain seems to be sagging in some gears. I took it to my mechanic and he informed me my B-screw is adjusted correctly and the chain is the correct length. I can remove the sag by tightening the B-screw, but then shifting becomes very poor. My mechanic thinks the derailleur is damaged. It's a brand new bike, so maybe it got damaged in shipping?

https://youtu.be/cBRX3CLebGQ

I'm talking to the manufacturer to hopefully get this sorted, but I thought I would get a second opinion here while I wait for that to get figured out.

Thanks.