u/Appropriate-Board543

I’m trying to refinish this ikea Gerton (100% beechwood) and I already used Klean strip premium stripper to remove poly and I tried to sand off the old varathane classic penetrating stain in dark walnut (oil stain). I did not use a pre stain conditioner when originally finishing this. There seem to be some dark blotches that don’t sand away no matter how much I sand at 80 grit. I want to restain again with dark walnut, so would applying another dark walnut stain even things out or should I still try to remove this by sanding more or something else? Would this prevent a new stain from curing properly?

My sander keeps sanding the most in the middle, and even after replacing the pad it has the same problem. With how the sander works, there’s a spinning mechanism in the center that bulges out, and if I screw the pad in all the way tight, it starts to bulge out in the center of the pad. If I loosen it, the pad becomes flat but it wobbles like crazy and sounds like it’s rubbing against the rubber. Is there anything I can do?

I’m finishing this desktop using varathane ultimate water based polyurethane in a matte finish and it’s been 9 days and it still feels soft and has some friction to it. It also scratches easily with my fingernail. I put on the first two coats pretty thick and realized it after, but sanded it with 300 grit and applied a thinner top coat with a foam brush. It felt much better, but it’s still not feeling hard after 9 days. It was applied over an oil based stain (2nd picture) that had 4 days to cure that felt smooth and dry to the touch but picked up some dry pigment on a rag, which I thought was okay. Is this ruined? Should I redo this properly from the bare wood?