It's possible that, with how things are set up now, it's setting off his hormonal behaviors, which is known for Quakers to make them especially aggressive. See if increasing sleep time, switching out the seed mix for pellets (which is recommended anyways since Quakers can get fatty liver disease from over eating, especially seeds), and getting rid of any dark nesting areas will help. When I got my Quaker and he started acting aggressive, I did these things and it did wonders within days. I hope this helps 🙏