33'' Zero Turn Deck

I have a 33" Yard Cruiser, I am the original owner, it has ran, and mowed perfect until this year. Every so often while mowing I have blades of grass standing back up, I have even tried mowing half a swath to see if that will help, it doesn't. I have an in law with the same deck on a newer zero turn, and does the exact same thing. New blade has been installed, deck has been adjusted. I don't know if the blade speed is slowing down, anyone have this problem before?

OK so I will tell you what I have been seeing this year. First of the year all was good. Grass cut very well. June Ish and grass was still getting cut but would lay down under my tires. I changed from G6 to high lifts. All was good again. Now as fall is upon us I am running into the grass not being picked up everywhere. So i have to redo a few picky customers yards. It is the grass. I compared some pictures of the grass from April/May to now and all the blades are much skinner. The grass has lost a lot of weight from what I can see. If you put any weight on it at all it lays down and some of it does not come back up in time to be cut. I have yards being watered and fertilized doing the same thing. No idea what is causing it.