DIY defect repair- What would Penny Do?

Hello Penny. We have a small but nagging problem.
Though very small we would love to have your expert opinion and direction on how you might tackle our DIY challenge 

We had new red oak conventional red oak HW floor installed late 2015 and our older existing oak HW floors refinished with a home remodel addition.
We were told that the contractor used Sampson coating varnish.

There are handful random BLISTERED spotty areas in the kitchen, smaller than a quarter coin, where the newly installed floors have the sealer coating degraded and bubbled in the actual floorboard seams.
Problem does not seem to be happening on the older HW floors that were sanded and resealed.

Not exactly sure why.

My suspicion is that they were not coated enough unless boards were not acclimated properly.
The contractor did send someone out once to readdress the situation.
They spot sanded and spot resealed. We hoped it was a one and done- we didn’t carefully observe his process. 

We tried to remedy a “spot” recently but it was a trial and error attempt that was under an area carpet. Less than perfect results trying to match the cured sheen exactly.

Since we are not ready to reseal the whole floor yet....if this was your floor how would you go about sanding and resealing in a spot fixing fashion?
We would love to get rid of the few random floor pox....if it’s possible in a homeowner DIY fashion to hold out tackling a total floor rejuvenation.
Knowing proper steps and sanding technique might be helpful.
The GATOR skinny sanding tool looks to be perfect  for our spots.

The photos attached are close ups.
Hope you had a nice Thanksgiving.
Thanks for reviewing our issue.

Kindest regards