I just joined this forum and I have been experiencing the same issue on my 2015 Craftsman T2200.
The belt controlling the blades has come off the pulleys occasionally since new but since it only happened five or six times a season I had not done anything about it. (it pops back on easily)
I recently went to the Sears parts store and we went through the detailed manuals and they advised that there is no adjustment on this model. I bought a new belt so we will see what this season brings.