Hello and welcome from me too.
Oh my goodness you do have a lot of things going on with your dogs right now it sounds like.
I agree that I think I would want to see a specialist, especially about the muscle issue, which may or may not be related to high cortisol.
Since that pre is fairly low, I would think about trying him on a lower daily dose. Maybe 20 or 15 even. And see if that will keep it low, but not too low. It can be a real balancing act to find what works And what keeps them comfortable.
Again, welcome to the forum.