It is hard to diagnose the patient when not in the office, but...
If the forestock has not been reduced too much underneath the bands themselves (which sometimes can be built up with cardboard shims)...
You can pop out the band springs and insert some shims into their mortises. A sliver of wood will raise the spring height and catch on the edge of the band more securely (or prevent the spring from being compressed as easily). Some lads use the "shaft" from a matchbook match with its head cut off. Then put the springs back in place.
Longer lasting "repairs' can be made by gluing wood shims in place.
In gleichem Schritt und Tritt, Curt Schmidt
Not a real Civil War reenactor, I only portray one on boards and fora.
I do not portray a Civil War soldier, I merely interpret one.