Looking for ideas on why my dog showing is for a new behavior while I wait to see the behavioral vet

hi thank you in advance, any ideas or thoughts is much appreciated.

my dog has a long list of issues and we have seen quite a few trainers and he is currently on Trazadone. I am on a waitlist to see the only behavior vet in my area looks like online group orientation is a 1-2 month wait and the evaluation will be 2-3 months after that.

my dog has been fearful of strangers since he was 1. I have a routine when guest come over to get him comfortable. He always gets his medicine and his thunder jacket among other introduction techniques.

I hardly have anyone over because of his fears but sometimes it’s unavoidable. within the last 6 months he has started to try and bite guest when they leave my apartment. the first time caught me so off guard he nipped my friend who he has known for awhile before I could pull him off. He didn’t break skin but still it was very scary for everyone involved.

since then of I have someone over before they leave I put him away in the kitchen using a baby gate. he barks lunges snaps and throws his body at it or will try and jump over it. he is 50 pounds so it very possibly he could break it down. I thought maybe it was quick visits like when someone grabs something for me and is only in the apartment for 5-10 mins but the most recent was during Super Bowl so several hours. he will even cuddle with the person for the duration of their visit and then flip a switch.

is he suppressing his fears until they turn their backs and he feels safe to attack? I’m just confused with the timing of it and I haven’t seen any post discuss a behavior like this. I obviously now have a no guest policy to ensure everyone’s safety until I can see the vet.

again any ideas are appreciated.