My 5 month old Doberman Male sometimes is jumping and bitting me

Hello and hope you guys will understand the situation because it is a little bit hard to explain.

So sometimes my dog will go full demon mode on me out of nowhere and jump and bite a little hard my clothes, hands, legs and leash. He is doing this when he doesn t get something from my hand or i don’t let him do what he is doing(bad behavior from him that he knows that is not supposed to do).

On my girlfriend is not doing this behaviour.

I do not react and I m neutral when he is doing this and I let him know that this is not what he is supposed to do.

I will put him in a sit possition with a little bit of force and don’t engage him for 1-2 min and he will sit quietly with no force but he is going full demon mode again and again until i just quit and put a muzzle on him and he just calms down.

I do not know if I m doing something wrong or I should just have patience.

This behavior started 1 month ago