loose belt

I have a Troy-Bilt 42" riding lawnmower, Model #: 13AK78BS011. It was working but the drive belt kept coming off when I would turn off the mower. When the PTO lever was not engaged, the belt looked extremely loose. I also have the belt retainers on close to the pulley. So I took the deck off and...

I attached a link of my mower deck belt, does this seem too loose? Any suggestions? This is my 3rd belt and I think it’s rubbing somewhere causing them to snap. This is a Snapper spx 48” 2691346-01. The manuals I had found aren’t much help but the deck diagram matches and everything is where it...