The attached photo is of a FPE Stab-lok panel located inside a wood cabinet inside a bathroom less than two feet from a sink! Beside all that :D, when I touched the front cover, the nearby light flickered (no sensation of shock or anything else), is the light flickering and indication of the lack of grounding?
Given the poor contact area of the buss stabs the breaker could just be that loose on the buss. Sometimes you can have breakers just fall out of the panel when removing the cover.