I had a similar problem with my front quick hitch when it was new. I was ready to start filing the opening bigger. (Arghhh....) After studying if for a while, I decided to loosen the big nut on the pivot bolt. Somebody had really over-tightened that nut. And it is a very unusually sized nut. In metric, it is somewhere between 27mm and 30mm. But my sets don't have 28mm and 29mm, so I can't help beyond that. SAE 1 1/16 is too small, but 1 1/8 is loose, but might work. At the time I ended up putting a pipe wrench with a cheater pipe on it. And it still took all my strength to get it done. But once re-tightened to a reasonable torque, the pin fit just fine. No problems since. And no filing.Removed the snowblower and put the front blade on . Had a heck of a time getting the pin out of front quick hitch so I could use the front angle blade.
Before putting the blade on removed the ring , on the bottom of the pin. Pin would not pull out, so put on the blade and plowed the front driveway. Still would not , guessing the pin was frozen in place. When I finished the driveway , I found a piece of metal about 4" H and slid it under the quick hitch and used it to break the pin loose. Great pin came up apx 1" and still wouldn't come out . After moving the quick hitch R-L a couple of times it finally broke loose .
By that time the rain had pretty well taken care of the maybe 1" overnight snow.