Can't speak to the stripe problem directly, but it is recommended for improved cutting that the front of the deck as measured at the blade tip, be 1/8 to 3/16 of an inch lower than the back of the deck as measured at the blade tip

Orginal Blades???(if so you probably need new blades due to blade tip wear???) IMO either blades are worn on the ends (tips) or the timing between two blades needs to be adjusted (move one blade in relationship to the other) If orginal blades they are probably worn on the ends enough to alow small strip of grass now not to be cut. Sharpen has no effect on blade tip wear 1/16" could make difference IMO. take that times two and you make see the enough to alow the thin strip of grass left between the blades???

OP - 1. Really tall grass can cause that problem by itself. Might try raising mower deck up to higher setting for first pass - then lower back down for final pass.
2. leveling deck fr to back per manual can help. As noted above, front deck lip s/b lower than rear when measured at blade tips.

3. Worn/damaged blade(s) might cause such, particularly if thin uncut strip is left between blades as RC points out. Also not too hard to install a blade upside down by mistake.

I'll level with the front a little lower and try.
but the blades seem to be square on the ends so I think they are ok.

And the reason I don't think its the blades is because the uncut strip is under the right spindle, not in the middle of the deck where the blades meet

Good advise above. I didn't see anything about scraping the deck clean- so there's my 2 cents!