Trouble with a canopy lock on a trailer.

I've got a trailer with a canopy that has four recessed locks with folding handles.

My problem is that one of the handles is so tight to unfold it takes two hands and a lot of strength, (something I lack these days), to open and close.

It looks like a fairly standard type lock with a locking lever sitting between 2 nuts on a threaded bolt connected to the handle, turn the handle and the lever turns etc.

When turning the handle it feels like its binding.

There is a piece that looks like a washer with spokes just above the top nut and hard up against the bottom of the recessed bit below the handle, but when I tap it with a punch and hammer it turns but does not loosen.

If anyone can understand the above and can tell me how to loosen the handle I would really appreciate it.