Westlock latch bolt does not retract completely

When I turn the door knob, sometimes the latch bolt would not retract completely. When that happens, the door cannot be opened. This applies to both entering and leaving the house.

When I am inside the house, if I turn the knob fiercely a few times and the latch will work again and the door can be opened. The trick does not work when trying to entering house with a key.

Obviously some part is not functioning normally.

How to fix it?