High squat mobility, poor control. This is more common in females, but also in males who've played sports that demand extra mobility as a kid, or who have a lot of congenital joint laxity.
For these people, they need to focus on trying to control the movement more, which means slowing down and thinking about positioning and trying not to bounce through the movement.
Don't read this unless you want to get bummed out about how you've been training the wrong grips, rep ranges, and exercises for your biceps, your back, and your entire lower body.