this is how the job looked before any grout repair was done. grout will crack and chip away when tile is not properly bonded. it’s just that simple. replace the tile then grout or no warranty can be provided.
grout repair at loose tiles. no warranty due to the fact that grout is not designed to keep tiles from moving, it is designed to fill in the spaces between tiles. recommended replacement of all loose tiles for a warranty against failure.
short video of loose tile, any grout repair will most likely fail very quickly