Field-strip your 97B and ensure that the magazine catch spring screw (#35) is screwed down tight. If it is not, the trigger bar spring (#34) might not be properly pushing up the trigger bar (#7) and causing it to not fully engage the sear (#11) when the trigger is pulled.
If it is necessary to tighten the screw, make sure that the curved ends of the trigger bar spring properly engage the grooves on the underside of each "arm" of the trigger bar.
Hope that helps!
DL