I think this may be down to absolutely rubbish quality control at the factory. As we say in UK:- "If you pay them peanuts you get monkeys." As we all know monkeys are not the easiest to train to make high quality goods.
I actually used a Kiev 4a fitted with the standard 50mm F2 lens (Zeiss Sonnar copy I believe) and the resolution on that was incredible, but the actual camera was quite frankly unreliable, to the point of being almost unusable

