Burr in paw??
Sounds like fear.
Still not acceptable.
A whelp would alert the good Samaritan.
He bit twice on the arm, breaking the skin and also bites while in the bed, breaking the skin.
I can’t really say since I wasn’t there and I haven’t met the dog but it reads like there is a fear of the dog (having teeth removed?).
Once there is fear, there is tension and the dog will feed off that tension.
I am understanding that it is a rescue dog, too. There are too many good, stable and needful dogs to live like what I am reading.
Mostly though, I don’t deal with biters. Dogs want to please and it’s my job to give them jobs to please me over. Some dogs just won’t connect and that’s always sad.
I would look for a Dobby rescue and talk to them. A vet check and if not neutered, I would try that.