I recently got new panniers (specifically these) because my old ones were falling apart and I have been having trouble attaching them to my rack. I've included some pictures at the end of this post to help with describing my issue. Specifically I am confused about using the bottom plastic hook that's meant to secure the bottom of the pannier to the rack. It is different than what I am used to from my old panniers but seemed like a common design when I was shopping so I didn't think too much of it.
However often I feel like the hook won't stay in place. A few times the hook has even come off the pannier altogether. The panniers didn't come with any instructions beyond the pictured "Adjustment Required Tighten Before Use". I assume that refers to this screw on the hook but I've tried tightening the screw regularly and it doesn't seem to help that much. Is there something I am missing?