There is nothing wrong with your pchain, hip flexors, mobility etc. You are just very very weak. That's nothing bad though. On the contrary, it leaves you huge room for improvements. 120kg in the leg press is extremely weak. But it makes sense too, because according to a rule of thumb the leg press should be 2*squat, which is accurate for you. My advice is : You just need to stop over-analyzing and trying to find a magic missing link that will suddenly release a huge squat. Take a step back, forget the 60kg. Next time squat with 50kg, or even better 45 kg. When you can do 3 set of 8 reps, advance to 47.5 kg. Then 50, 52.5 , 55, 57.5 etc etc etc till kingdom come.