I am so sorry for your loss. I still cry over my losing very difficult but extremely devoted Basenji, Ella.
My b Simba is about 5 years old, about a year and a half ago we got him neutered. Before he was neutered he was fine with everyone. But after we got him neutered he began to attack people. He dosen't do it when people come in the house, he only does it when they go to leave, or if they are in the house and make a sudden movement (ex. walking across the room, standing up)
He has bit my husbands brothers, and his mom, and some of my husbands friends that have come to the house. He has broken the skin on my husbands brother and torn holes in his pants. I have resorted to putting him in the bedroom when people come over. I am afraid he is really going to hurt someone, and we're going to have to get rid of him. This has only been going on for like a year and half and i have no idea why he does it. And its been getting worse, he will run around the house and start panting really hard if there is someone outside that he cant get to. But like i said when people come in the house he's fine, he'll let people pet him and he'll sit next to them but as soon as they move he attacks. Please if anyone has suggestions they are greatly appreciated, I have no idea what to do!
You might want ot contact a behavior specialist.
But in the meantime I would suggest working extra hard on obedience, or reinforcing the obedience he once learned – get him to sit-stay before people leave or maybe use a head halter and leash while people are at the door. Maybe as people get up to leave they give him a treat. Have you talked with your vet about his behavior too?
When was the last time he was checked by the vet. If the biting came on suddenly, it could be he has a medical problem of some sort.
Has he had a full medical check up? Especially a full Thyroid panel done? I really would doubt that his being neutered has anything to do with it… certainly I have never heard of that before.... but I would first get a full medical done (including an eye exam with a Ophth), with full blood work and full thyroid panel (which typically must be sent out separate from normal blood work that your Vet might do) and then contact a behaviorist to work with him (and the family).