@Kathleen Marineau The lock system was not fully engaged at time of install. This is the biggest issue with gaps like this. A laminate has a quick fix...vinyl not so much. A laminate repair kit (Bulldog tool or "Unifix" tool will work with laminate...but vinyl has other properties that make it difficult to achieve using just a tool). The variation in subfloor (not a flat surface) will ENCOURAGE the lock system to "disengage" or let go. The floor then "walks itself" apart (every time you step on it it moves a snick more). The short edges give away the issue. If this were SOLELY to a wavy substrate the LONG edges would be letting go as well. But they seem fine. The SHORT edges indicate an install error at the time these were put into place. Short edges "feel" like they snap in nicely. So people forget to give them a good "tap tap" when installed. The long edges are bit more difficult to maneuver so they ALWAYS get a good "smack" from the installer. And that is the difference between short edges "letting go" and long edges letting go. I see this from time to time with cork floating flooring. Same issue. If the floor starts to disengage it is 99.999% the short edge. And the reason: Not enough force applied to the short edge when it was installed. With so many short edges that are disengaging, I suspect you will need a full "remove and reinstall". A single plank can be dealt with using a "tool". But with 5-6 in a single space...it requires a redo. It is possible you have multiple issues...the sag and the uncontrolled Relative Humidity have added to an initial install issue. You can fix the sag...and reinstall the same flooring or you can work with a sheet product.

According to this person it is Formerly known as Allure isocore, so maybe we can find more under that name :) http://justcallmehomegirl.com/lifeproof-luxury-vinyl-plank-flooring/

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Never use installers from big box stores. My story. To save some money, i had Lowes install a $ 2 SF vinyl floor. The 5th party installers laid the planks over a needed drain. Due to the location, I never looked at the area. After 4 months, water started coming through the planks. It turned out, with the drain blocked, the water went behind the baseboards, then under the vinyl planks. It took 4 months to start coming through the plank seams., I called Lowes, and my insurance company. The insurance company immediately sent over a restoration company. All the walls in the laundry room had hidden black mold, inside the walls. Walls and floor had to be ripped out. Surprise 1. This is considered concealed damage. Concealed damage, whether known or unknown is no longer covered by insurance companies. In other words, you have to spot it within a few weeks. Surprise 2. Lowes subcontracted to their national subcontractor. They then subcontracted to a local flooring company. This company then subcontracted it further. Lowes wanted no part of the issue, and told me to deal with the subcontractors. At one point, I was told the installers insurance expired and I was out of luck. It took a small claims court notice to get their attention and finally paid. I just signed a contract with a family owned very reputable local company, whose installers are employees of the company. That’s becoming very rare. I’m getting Karastan Luxury Vinyl Planks. Both the planks and installation are significantly more than big box stores. My few cents,