142Highlander,
The CF valise, with the strings on the side, is very slippery, and if it‘s not tied down very tight, it will slip and shift during a ruck march.
One solution I use, if I have the time, is to run the valise straps through the strings and keep it as centred as possible, and zip it tight.
Check that you have run the valise straps correctly, too. They should be pressing the valise into the frame, not totally wrapping around the valise. I see people all the time have it running around the valise and basically hanging between the plastic buckle on the ruck bag and the metal frame on the bottom, so it is basically loose between the ruck bag and the bottom of the frame.
The valise straps should only touch the outside of the valise, and when tightened, it will press the valise against the frame and bottom of the ruck bag.
Hard to explain, easier to show! But I think you probably get it.
If you haven‘t already, make sure your webbing is set up correctly, too, so the buttpack isn‘t bumping the valise off-centre all the time. It‘s amazing how many troops I see with their buttpack put on all wrong, and it ends up riding too high and interfering with the ruck.