That blank shot can indicate that there is a leak in the cloth shutter. Go into a dim room, let your eyes adjust, and shine a flashlight through the front of the camera with the back flap up to check, then wind on and check again. If you see those little bright dots, then you have found your problem. Those frames that skip can be explained if you shot in a fast succession a row of images where a tiny light leak would have not seriously affected it, or if you shot a series in a darker setting, such as at night or indoors, where there was not enough light intensity to have marked the film.
If this is the case, the diy remedy is usually some black fabric paint, and i have heard of people using plasti-dip as well.