If that's just some material fraying from the edge of the bag I'd use a lighter [carefully] to melt it and stop that from happening. Not a big deal.
If that's thread from the stitching coming loose it will eventually come totally loose and needs some repair. If this is the case and the bag is still under the 5yr warranty you can chat with Ortlieb or you dealer about getting it sorted - although it might just as easily to get fixed yourself.
Worst case if all the stitching at that edge were to fail you'd just lose that plastic stiffener piece. The bag would stiff close and be waterproof.