Help- what's wrong with my scag deck?

I'm having an issue with my scag tiger cat 61" velocity deck. The closed end of the deck is leaving a small "brown strip" of grass . I've tried new blades, sharpening blades, different mowing heights and speeds and it's still a problem. What is wrong? It's making all my lawns look bad. Only been happening for a few weeks as far as I know. I will try to attach a picture.

Thanks in advance!