My guess will be the wrong angle.
You remind me many years ago. I couldn't shave properly on the neck area.
Don't insist on the same areas.
Don't chase the perfect shave.
You may want to try a more aggressive razor, but from what I read it is possible to cut harder yourself.
I suggest even more light hand and watch carefully when you lose the angle. You have razor burn in the same area because you approach the hairs from the wrong angle or the hair there is not short enough to be cut properly.
Gillette Silver Blue will be your friend in this case. Avoid Feather, the king of harshness, I don't really get that hype around this blade. It is insane.
Oh and a thought for the neck. Try to stretch the skin in this specific area and lay the razor VERY lightly and take the hairs at once. Don't go over there more than one time.