One of our customers asked me to look at a floor tile problem he is having.
The tiles are 12″ x 12″ installed in the entry hall. Installed about 15 yrs ago, new construction.
There is one area about a 6 inch diameter where three tiles meet that the grout has come loose several times. Each time he re-grouted the area the grout came loose after a few years. The rest of the floor has had no problems .

I tapped around the area  and and it seems there was a poor bond between the tiles and the substrate. The rest of the floor sounds solid.

I found this product on Amazon
Tile Rescue Injection Repair Adhesive 10.5 oz. Tube – – Amazon.com 
Wondering if anyone has tried it and what the results were.
Or if there another product or repair method .

Thanks