The causes can be one of these:
1. Poor form/technique - have someone record your squat and share it with the group. A side angle view would be best. Do not go all out. Take slightly lower weight and record the footage.
2. Poor progression scheme - You go all out every squat session and do not allow the body and joints to recover. Take de-loads and train light for some weeks before building up again.
3. No warm up - You jump to heavy weights. Warm up appropriately to have blood flow and a raised body temperature.
4. Exercise order - If you are doing other heavy compounds before your squat, change the order and push squat over everything else.
5. You can also use knee sleeves/knee wraps/belt to support your joints and abdomen while doing such heavy loads.