Latch lever use to stuck while attempting to lock the door

A home owner from MA says:
I have issue with latch lever. If I move the lever to more than 30 degree angle, I will not be able to lock the door. To lock the door I need to manually move the locking mechanism such a way that it is slightly below the catcher in the frame and latch around 30 degree. After that I am able to lock the door. Is there any fix for this ?

I also tried to open the lock by removing the top and bottom screw of latch lever plate, but can't pull out the assembly. Need to know how to pull it safely without damaging the door.

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Paul from SWISCO responded:
Welcome to SWISCO. The reason why these thumb locks normally break is because the internal mortise lock 82-037 needs to be replaced as well, not due to any fault of the thumb latch itself. I hope that answers your question.
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