My tile adhesive doesn't stick to the backerboard in some parts. Why?

I am tiling my floor and I am using TEC Invision Tile Adhesive. When tiling, I er the back of the tile with the adhesive and then apply pressure as i place it to the floor. I make sure its stuck well into the backerboard and I let it dry for a good 24 hours. When i went back to the areas where i tiled i felt some shifting tiles and i pulled about 5 tiles up. These tiles had all of the adhesive to the back but not one drop of the adhesive even dried on the backerboard. The backerboard was completely dry and was just how it was when i started tiling. I am completely baffled on why this happened and I don't think ering the back of the tile has to deal with it because it is said to hold better. So why is my tile adhesive not sticking?? I did a whole bathroom doing the back-ering technique and i have had no problems until with this tile adhesive. I was using Ker 909 before and Type 1 tile adhesive.