
He is a teenager, and like hunman teens has discovered that he can. He is pushing boundaries and assering independance.
You need to go back to the drawing board with training. Never give him the opportunity to disobey a command. So start with making his recall on the lead 100%. Then proceeed to do same in the house, in the garden, then on lead with distractions and so on.
GSD's can be very one person dogs, and running home to find hi MUm is probably him worrrying about where you are, and again because he can.