Chain slipping, rear axle loosening

Howdy folks! Only 1 small issue with my 1987 fourtrax. (Chain drive) I’ve slipped a few chains now and think I’ve found the culprit.

Typically it is just while going through tough terrain, sticks, deep mud what not that this happens. I just had it happen again this afternoon and noticed something odd.

I put it in neutral and began messing with the chain. I noticed the entire trailer hitch was about 20 degrees from vertical and the chain was tight. I forced the hitch down towards the ground which loosened the chain, I pulled the quad backwards and fed the chain back onto the sprocket, returned the hitch to horizontal (which semi rotates the rear) and it tightened the chain and I was able to drive home no problems.

Anyone know if there is an adjustment rod or what not that would cause the bracket/axel to rotate freely?

And sorry no pictures, I’m using my cell phone as my internet is real slow today!

Cheers, thanks!