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.
related posts
3 Tricks to Increase Maximal Strength
If you've only been training for a couple of years, just about anything you do in the weightroom will make you stronger. However, those of you who have been training a bit longer need to pull out the heavy artillery.
Top 10 Deadlifting Mistakes and How to Fix Them
When a guy who can pull 800 pounds in his sleep talks deadlifting, you'd better listen up and take notes.
Tip: The Missing Exercise for a Stronger Bench
It increases stability and reduces shoulder pain too. Check it out.
Louie Simmons on Explosive Lockouts
A lack of explosiveness has killed many a deadlift at lockout, and no one knows how to fix it like Louie Simmons.