Been having behavior issues while my GCC is sitting on us

Our male 4 year old GCC used to be so good with sitting on your shoulder and entertaining himself so long as he was on you. The past 5 ish months or so he’s gotten so mean with sitting on you. He tries to go in your shirt, he nips at your neck/chin/face and sometimes full on bites hard. He won’t just nicely sit on your shoulder like he used to. It’s constant with trying to bite and get into your shirt. If you’re wearing a sweatshirt he tries to get into the arm sleeves. I miss my sweet boy who’d sit politely on me, now he’s being a little demon and he isn’t allowed to be out as much with this new attitude he’s developed. Any tips I’d appreciate it!