Did you use any binder in your sausage mix? I made a batch of bratwurst using venison and pork. The first time I made it, I didn’t use a binder. The fat cooked out of the sausage and left empty pockets where the fat was. Then, I learned about adding a binder to the bratwursts. For Bratwursts, I was encouraged to use carrot fiber as the binder. This made a huge difference in the texture of the meat. There were no more empty pockets where the fat cooked out of the meat.
For summer sausages, they recommended using Sure Gel. That made a big difference in the summer sausage. Since you are making a premium sausage, they encourage you not to use any other brand than Sure Gel.
Hopefully this will help you out as much as it has helped me.