Solid Hardwood, Engineered and Laminate Flooring - Strange uneveness in finish

I am in the process of refinishing my hardwood floor. I sanded it down well. Applied a coat of sealer, screened it, then applied a coat of polyurethane. I noticed in front of the windows I had to sand it more aggressively because of more uneven boards. After the first coat of poly dried I noticed that in the area in front of the windows it looks like I didn't even apply any poly. There's no shine there and that's where I applied it the thickest if anything. Is it possible that because I cut the floor down slightly more in that area that the coating soaked in more? After I applied the sealer those areas didn't look or feel any different than the rest of the floor?
Will an aggressive screening before the second coat of poly help to homogenize the whole finish?
Any advice on how to rectify this situation. We're not looking for a super pristine finish or anything. The house is being sold soon.
I'm a little worried, I don't want to have to rent the drum sander again and redo the whole floor.
Thanx
Jim

I don't have much experience, but been reading too much as I have been working on my own floor. I would lean against agressivly screening. Did you agressively screen by the window after the sealer? Why was a sealer needed? Agressivly screening is only going to set things back. You may need consider a third coat of poly.

Sealer was needed because I was always taught that you need to seal the floor for 2 reasons. One being it's not wise to leave a newly stripped, naked floor exposed to the elements for any length of time, especially in my area where the weather is a little more humid, it's best to seal the floor same day as sanding. Also on a wood like oak which has a very coarse grain the poly will soak into the unsealed voids in the wood lleaving a finish that's coarser and requiring additional working to get smooth. I did not screen more aggressively by the windows. Just went over it real quick to knock off the "wiskers". I don't mind setting things back a little bit if it will mean a better finish in the long run. I just don't want to drum sand it again.
Thanx
Jim

Also I think the flooring is really cheap too. I have a piece I'm refinishing by hand because when I pulled up the T-holds between rooms a piece of flooring came up along with it. Upon further inspection I noticed the oak was a much coarser, open grain material (almost like what we used to call swamp oak). And no amount of sanding got rid on the grainyness.
The sealer(basically shellac) advertizes that it completely seals the pores in any wood. Well not this time.
What can I do???
Help!!

Jim

You sanded the areas differently then the rest of the floor, and sounds like you burnished the areas with aggressive force.