But, there's something that can happen with strong-willed, and especially intelligent, dogs. If you have to maintain your top-dog status pretty regularly, and then, for some reason you are feeling stress, tiredness, sadness, etc. and that same dog detects it, they can move straight back into the role that you don't want them in.
That can include protector, and other things. I've seen it in the form of scanning before, growling and/or barking, rushing the fence or against the leash, etc.
As I say, it might be something that you just can't see or hear, even people fighting in their home.
But, try being your obviously top-dog, assertive self, not letting him get by with anything, and see if anything changes. You may not feel that you've been showing anything which he could mistake as weakness, but their signs can be different from what we think of, and Charlie's an astute dog.
Good luck, let us know if you learn anything.
Love All Life, Thank You For Posting! :)