This is a new construction home. The floor installer and his crew are installing engineered hardwood throughout the first floor. The floor flows from room to room.

For whatever reason, in the master bedroom they used all the same length planks every other row for the first 12 boards or so, which crates a zig-zag pattern. From then on, they started making the boards random.

We also found a board within the zig-zag patern that doesn't seem to be nailed to the subfloor. You can see the floor flexing in the video below.

Should I fight with my builder and have him rip up the floor and replace it? Is it possible to just rip up the 12 or so board, leaving the rest of the floor in place and replace those?

You can see the pattern in the floor in the attached images.







https://youtu.be/SD3-0aMSGDE

Yeah, all those H-Joints (pattern) are not a recommended installation method unless someone specs it like an architect. You may see that pattern in a commercial project thats spec'd that way.
And if fastened there should be no movement.

The trouble area can be removed then re installed in the opposite direction provided installers use a spline to reverse the direction.

Yes, I would have them replace that. Those H joints aren't good for expansion/contraction and they don't look good.

Debbie Gartner, The Flooring Girl
http://TheFlooringGirl.com