Why did you sand anything? IMO you might be using the wrong roller nap for the job and going back and forth with the roller too many times.

Looks like your sanding did the damage, it needs a fresh skim coat now it seems, but first I would try a regular flat pole sander (palm sanders are very uneven) starting with a medium grit and repeating down to a fine drywall grit, it may take several times. Then wash that dust of the walls at mleast twice before repainting.

I suspect patching without priming as a base coat before painting. Spackke absorbs paint differently than an already painted surface. I'm unsure of the best way to smooth a painted surface but you can add a coat of primer and repaint.

Hello all....thank you very much for your prompt response! First, to answer your question Patricia, I didn't really sand much, was told I was supposed to to keep things smooth, yet regardless, it looked exactly the same pre-sand. Also, I had used a 3/8 nap from Wooster Wool. Rnonwheels, as I had mentioned earlier, I really didn't do much sanding, and that discrepancy with the paint was definitely there before I started sanding. As you know, will sand as much as I can in preparation of another coat. Thank you for the tips on getting the dust off! Lastly, thank you tdemonti. So you would suggest I prime the whole wall again before adding one last coat of eggshell? It wouldn't be prudent to make sure that the walls are smooth & simply add another coast of PPG eggshell?? Thank you so much again for all of your comments! I can't wait to make this wall look good!! Definitely the last time I'm using eggshell on an interior wall....the rest of the house was painted ENTIRELY in Sherwin Williams flat white and looks gorgeous compared to what I am dealing with here....thank you all again your individual input has truly been appreciated!! :)))

@HU-650181179 I presumed you painted directly over spackle that you sanded which would cause the surface to look different from painting directly over paint. I was taught to spot prime where I would spackle - for adhesion. Spackle and sand until you achieve a smooth surface. Remove all dust.

Prime the entire surface before painting for a uniform base coat.

If you painted over dust, I'm unsure if that can be sanded smooth. Cars are painted in a dust-free environment.

Get your wall smooth then prime the entire surface for a uniform basecoat before painting regardless of sheen.

Here's how to address roller marks - https://www.ppgpaints.com/pro/pro-painting-tips/how-to-fix-roller-marks-or-excessive-stipple-in-pa

yeah, you can't really paint spackle or drywall -- they suck up paint differently. prime the damaged zones and some distance around, then paint again.

I think you have the same issue as the poster whose ceilings were wavy. It might be a wavy drywall issue and those lines are the studs.