Actually your squat numbers aren't bad so it's not a weakness in the legs.
On your Overhead Squats, try moving slower on the descent. Maybe give yourself a 3-4 count until you reach your full depth. Make sure that you're keeping your back engaged throughout.
Also, you can try holding the bottom of Overhead Squats/Snatches/Snatch Balances/etc. for 2-3 seconds before standing up to further develop the comfort of the bottom position.
Isolate your weakness and let that carry over into the lift.