Your floor is not flat so the flooring is holding itself up by it s own will and when you walk on it you are pressing it down into those valleys and it s touching the concrete.
Luxury vinyl plank not sitting flat.
During installation run a vapor barrier under the vinyl plank flooring to help prevent.
The luxury vinyl materials are less likely to buckle than some of the less expensive economy tile floors.
Vinyl plank is water resistant and is not like hardwood which is not resistant to water.
When not installed on a level surface a luxury vinyl plank floor can shorten in length when it rides over high and low areas and it can also lift on edges or ends where a substrate irregularity.
Floor prep the only major rule for installing vinyl plank floors is that the surface needs to be flat.
That is my semi educated guess.
Vinyl plank flooring over radiant should not be a problem provided you follow the manufacturers recommendations.
And i don t like it.
After all a floor can be flat and have a plane to it.
If water seeps up under the flooring from an extremely moist concrete subfloor the adhesive can be weakened causing buckling in the floors.
Level is not necessarily important.
My new click lock floating luxury vinyl plank floor has some dips and noises i wasn t expecting.