Perhaps I left some stripper residue on those two sides. I'll clean thoroughly when I start again. Thanks!
I think you know what you're doing, but my process for finishing wood:
Sand thru 80, 120, 180 grit. Anything finer can close up the grain which makes it harder to apply stain.
Wood conditioner (same base as stain and poly...oil with oil, water with water, etc...).
Lightly sand with 220 to knock down fibers that stand up during conditioning.
2 Thin coats of poly. I don't sand after 1st coat because you can go right thru it into the wood.
Light sand with 220 grit.
Coat of poly.
Repeat until you've got 5 or 6 coats.
After final coat, sand it with 00 steel wool.
Rub and polish if desired, but I find the steel wool evens out the finish.
I wear a respirator for all finishing work (fumes from stain/poly, plus fine sanding dust are brutal).
I also make sure I have light air flow across the entire finishing space...open window at one end of room, box fans blowing out window at other end of room.