I believe the mag latch spring on the Buckmark is held in place by the right-side grip panel, so if the grip is loose it can cause problems with mag retention. Same thing can happen if the grips are removed for cleaning, and the flat mag latch spring is not properly positioned back into it's cutout in the frame before the grip is reinstalled (it will bind and not provide enough tension to the mag button).
The only reasonable connection I can come up with between the mag falling out and misfires with hits on the edge of the rim, is if the mag is not being held in place properly during feeding/chambering, then the top round might bind or fail to feed fully into the chamber. If it is 98% chambered, part or most of the energy of the hammer and firing pin is being wasted to finish chambering the round, and there may not be enough forward motion left to crush the rim and fire the round. Start by fixing the mag release problem, and if that doesn't correct the misfires, then look for another cause for problem #2. In rimfire semi-auto rifles and pistols, dirt/fouling/crud buildup is right near the top of the list in causing any functioning difficulties, so give it a good clean-and-lube session before looking for more serious problems.