The OP mower appears to be a 21" single blade self propelled mower.
It's been suggested, but I'd first scrape off all the old grass that's accumulated under the deck. That could cause this. It's good practice to do this everytime you change or sharpen the blades.
I'm not sure on this mower, but all rotary mower decks are designed to create lift (suction). Some decks have baffles installed in the manufacturering process. Maybe check to see if something looks like it was broken off or rusted off under the deck
My Honda has dual blades. The large blade does most of the cutting. The upper blade cuts some, but appears to help with the lift. The upturned parts of the blades are the lifters. They wear from abrasion. The deck is shaped to work with the blades to pull the grass straight up and cut it off at a consistent height. Mower decks typically are asymmetrical to help direct the grass out. So worn blades and the shape of the deck could leave uncut grass in one place like described.
A side note. I bought a real type manual push mower, because I bought into the idea of being more environmentally friendly. It cuts ok, but has a tendency to push the grass down leaving an uneven cut. It has no way to pull the grass up to cut it off evenly.