Troubled Toddler Turquoise

So I have a 4 month old Turquoise GCC that's been with me for about 2 months now named Luca. He's usually a sweet little thing that loves attention and is honestly kind of a velcro bird that just loves being with me and/or my wife. For some reason though, he'll sometimes bite our hands without any warning, then will puff up, yell, and keep charging at our hands. He'll just do this completely out of the blue and wont stop unless we hide our hands. When he bites, he bites hard too, usually enough to at least bruise or leave a mark, if not break the skin. Sometimes when he bites he latches on too until you can somehow manage to pull your finger out of his mouth. He's usually completely fine with hands too and steps up with no problem and even knows how to shake. He even tries to preen our fingers and nails sometimes and does it gently without causing us any pain. It's just sometimes he'll randomly get aggroed on our hands and throw a fit. I cant seem to find anything that triggers this either. He'll be preening on my chest while I'm on my phone, all happy and content, then the next moment he bites me, war cries, then charges at my hands again and I have to quickly hide them before I'm bitten again. Sometimes it happens after I ask him to step up. He'll step up liked asked, I'll coo and talk to him for a bit, then suddenly he's reaching down to the hand he's on and biting, usually latching on. I never went through something like this with my other conure. Is there a way to stop this or at least notice some warning signs? I've tried the bite pressure training which has helped with his normal bites but not these random attacks. I've also tried not reacting or just blowing a puff of air on him to get him to stop and nothing seems to work. The puff of air doesn't even seem to faze him. Any advice?

Does he have any pin feathers at the moment? My wife's Conure will behave exactly the same way if "you" catch a pin feather. Have a short piece of dowel ready and get him to step up on that and move him to the back of a chair and leave him there for a bit.

Parrots have a reason fir bites, try and figure out why
It’s easy fir GCC to develop fear of hands and see hands as. It part of us. I hand feed treats, pay attention to body language, if they don’t want to be pet or have attention don’t force it, sometimes hands moving to fast can freak them out, happens to my GCC even after 7 years together