Personally I don't think it's much of an issue because it appears only visible in the right light or light angle. The old saying in the business goes as follows when it come to addressing problems.
"Inspections shall be done from a standing position." In other words, if you can't see it standing up, there's no problem. I know that's not the answer you want to hear, but...
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you add another coat of poly and can also get some in between the grooves
That in itself could cause more problems, especially with a water based finish. And we have yet to even think about adhesion with all the new fangled finishes today in so far as bonding to the existing finish.
One outside possibility why this may be happening could have to do with the adhesive used. Years ago when I first used DriTac 6200 I didn't follow the directions because all the other adhesives previous to that were the type where you just spread then install.
Long story short, they recommended letting the adhesive "flash" which means allowing it to air dry for a period of time before laying into it. While this may not be the issue, it could open up some possibilities into why it's happening.
Without allowing any flash time, all the end joints showed exactly what you are referring to a few hours after they were installed. The problem was the moisture from the adhesive, but it did go away after a day or so.
I'm freely trying to grab what may be going on here based on that experience and especially the wrinkling characteristics. Perhaps these are ares where too much adhesive (for lack of a better term) is crammed between the planks and any water that is spilled does not innocently trickle to the bottom or dissipate. Nearly all hardwoods have some kind of microscopic gapping in the way they are milled for expansion and contraction.
SECONDS is the only thing that doesn't make sense to me because it usually takes time for the problem to show itself.