I had the same problem with mine. The nuts were not tight enough to frame. Took the cotters pins out and tightened the bolts and that solved it.. ( for me) Put new cotter pins back in.
Could you tighten the nut all the way tight and then drill a hole to put the cotter pin in? If you wanted to you could grind the extra off the bottom ??
Hate to say it but I have no idea. Problem number two is I can't post pictures. Tough getting old !! Mom tells me that every day and she is 100 years young ??