It does seem from your brief description that the dog might not have been feeling well.
That having been said, you should consider establishing the alpha female role in your dog’s mind. It does not sound as if you have all that much interaction, which means you have the opportunity to pull rank on the dog.
The crate should be safe, but if the alpha says, “Come”, the dog comes, even out of the crate. Then the alpha says, “Sit”, and the dog sits. If the dog seems agitated or frightened, the alpha says, “Stay”, and the dog stays for a few minutes while he calms down. Then the alpha comes and wipes the spit off him.
You don’t have to be mean or harsh, but you do need to establish that you mean business. The dog eats when you say so. If he pulls any crap, he doesn’t eat until he stops pulling it and submits. You own his crate, you own his food, you own his toys, you own his time and attention. He gets your stuff (food, crate, attention) when you decide he does.
Dogs usually bite because they are mean, scared, or trying to establish dominance. If he is mean, get rid of him. If he is scared, reassure him, and a good big part of that reassurance is to let him know that there is someone else in charge who will make all the decisions for him, so he doesn’t need to concern himself with that. If he is trying to establish dominance, merely show him (with obsessive consistency) that you hold all the cards.
Basic obedience training is a good thing. Sit/stay/down/heel/come, that sort of thing. The dog will be much more pleasant and happier if he understands that The Master has things in hand.
Regards,
Shodan the Veterinarian’s Son Who Nonetheless Trained All the Dogs in My Family of Origin