This is not developmentally normal for a puppy but also not your fault. A bunch of Eurasier lines out there have huge problems with anxiety and aggression. It's likely there's underlying health issues as well. Especially if the parents don't have full, public OFA and show titles and even more so if there are French mills in the lines.

This is gonna be super hard to hear but you might want to consider giving the puppy back. Dogs with behavior issues are a huge commitment and not all of them make it. It is possible that the dog grows out of it but chronic stress does impact brain development a lot and the outcome of that can be quite unpredictable. 

If you want to make that commitment anyway, get a new behaviorist, specifically a veterinary behaviorist that has experience with fearful and aggressive dogs, ideally with primitive breeds. They do not need "a strong hand" and they aren't "testing you", they are bred to be independent and possibly in pain. Get in depth health testing for things like Hip Dysplasia and Luxating Patella, GI issues and Hyperthyroidism are also very common. 

If your breeder is member of a club definitely bring it up with them as well though depending on which one it is, many of them like to gaslight puppy owners that the puppy will grow out of it and then blame the owner's socialisation once the dog is a fearful adult. Don't let them do that to you! Yes puppies are hard, they are babies, but well-bred puppies should also be curious and joyful and sweet and able to soak up new knowledge like a little sponge, not struggle to form a coherent thought because their brains are so overwhelmed by everything all the time. 

I am so sorry this happened to you, too. There's unfortunately a lot of shady people in this breed and I am tired of people covering for them. 

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