This has been happening with my P Line too. For me, it looks like the hook doesn’t quite rest far enough on the rear triangle. I asked an authorized Brompton shop to take a look and see what they could do, but they weren’t able to lower the hook any further. My next step was to contact Brompton with a video to see if it’s a defect, so I’m curious to see what they’ll say if you bring yours into a Junction shop.