I have butcher block counter tops that I just bought. Unfinished birch to be exact. I stained the block then let sit for 48hr. After that, I put 4 coats of wipe on poly on. It looks and feels fine except for one thing. When I bend down and look level with it, it looks like some spots didn’t take the shine as well. I’m looking to have and even shine on the whole thing! I did sand lightly in between coats also. (Side note) I did sand the block when it was bare with 220 grit sand paper. It was completely smooth and wiped down 3 times with tac cloth. PLEASE HELP!
This is perfectly normal with dilute coats of varnish, especially on something like the counter top material you bought where the grain direction, piece to piece, can be (usually is) so varied.
In some spots (e.g. around knots) the grain will be nearly at right angles to the surface, and these areas are much more absorbent1 than the majority of the wood, where the grain runs more parallel to the surface. In addition to the lower gloss in those spots you should notice they have a noticeably darker colour, from them absorbing much more stain than the surrounding wood.
In order to develop a completely even surface in terms of reflections/surface gloss you need to build up coats of finish until that happens. The thinner the finish2 the more coats it takes. There's no useful rule of thumb for you here I'm afraid — because wiping varnish and wood vary so much — so it's just a matter of keeping going until you get there.
This is just one of those things where it takes as long as it takes.
The following won't actually have impacted the uniformity of the surface gloss much or at all, but I mention it for completeness.
I did sand lightly in between coats also.
This is not normally needed, or desirable, when using wiping varnish. You sand between coats of any finish where necessary, and ergo not when it isn't.
So if the surface is good, and there are no 'nibs' or specs of dust adhering to the surface — which would be typical when using wiping varnish — you should just recoat without sanding. Sanding between coats is always a small step backwards from the final finish you're looking to achieve, so it should be done minimally3 or not at all if possible.
1 Close to or the same as end grain, which is famous for its absorbency which is why it so often looks much darker than the long-grain surfaces.
2 This means both the physical thickness of the coat as well as the dilution, which directly affects the first thing.
3 For example just two swipes with med/fine paper such as 320 or even 400 grit, with almost no pressure on the paper — some finishing experts recommend you use just the weight of your arm here. Sometimes you can even de-nib successfully with the rough side of brown Kraft paper, which is now my preferred way to do this.