I'm no bird behavior expert, but I have a green cheeked conure and I can tell you that a green cheek should not be in a cage like that for more than a couple hours a day. Green cheeks are high energy birds, it could lead to lots of stress and excess energy (which can come out as aggression). I don't know if the cage is what is CAUSING your bird to have behavior issues, but I can tell you that you will never make progress with him if hes stuck in a cage (especially one like that) most of the time. The most progress is usually made out of cage and in a neutral location in my experience!Update. Snuck a few photos while she was out of the house. Here’s a full view of Sassy’s cage. Sleeping hut is at the bottom and is green.
Excuse the mess, she cleans it once a week.
Sometimes hormones can heighten existing aggression, and small dark spaces like hide huts have been known to stimulate hormones. Not getting 12 hours of sleep, eating certain foods, and not getting enough light exposure during the day can also stimulate hormones.
make sure you are listening to the birds body language and not pushing their boundaries. Some birds will stop using warning signs before lashing out because their owner ignores them and only listens when they bite. neutral locations are your friend with birds struggling with aggressive behavior. Some birds will act completely different towards ppl in a new location. Target training is a fantastic off hands way of interacting with your bird, and it forms positive associations, I highly recommend it.
It's fairly common for green cheeks to avoid or even be aggressive towards less liked flock members (aka people who arent their "favorite person"). Some of this is natural behavior, and some of it is learned. These behaviors become concerning to me if the bird is OVER aggressive towards less liked people, or if they act aggressively towards the people they normally like. This kind of behavior is not normal and needs to be corrected. A Green Cheeked conure isn't likely to be totally friendly towards everyone, but they shouldn't always be aggressive.
I hope this is helpful to you!