LM5020: Over current protection issue

It seems your circuit is a flyback. The LM5020 over current limit is achieved by limiting the primary side switch peak current, which is not directly the output current. You need to see if you current sense resistor is selected properly. You also should not use a too large transformer but use an appropriate size such that it can support full load but not too much overload capability, such that it can more easily run into saturation to quickly raise the primary peak current to prevent excessive short circuit current on the secondary side.