I wonder if the tile has a resin surface which could be affected by chemicals or maybe the porcelain tile was an unglazed tile that was sealed?
The glaze on the tile is applied at about 2000 degrees F so you can’t re-glaze it. If it is a sealer on it then find out what sealer was used and reapply it in that spot to make it shiny again. Talk to your tile supplier and installer to find out exactly what type of product you do have. Good Luck!