I have an Arkel Bug that I attach to a Soma Deco rack on my Crosscheck. It was pricey, but it's a very solid pannier. I haven't had any issues with it slipping around.

I think the biggest factor in stability is the attachment to the side of the rack. On the OP's panniers, that's accomplished with a plastic knob. In my experience, those tend to slip around and off with unstable loads. I had similar problems when I used some old REI panniers that were set up like that. However, the position of the knobs was adjustable, so you might be able to move yours around to get them where they are a little more secure.

The Bug, OTOH, is attached to the bottom/side of the rack with a hook and bungy. Much more secure.

Riding aggressively shouldn't be an issue if the panniers are properly attached.