Ditto jt, Put your stripper down at regular dilutions but keep it wet for much longer than normal. I mean like an hour. Just spread it with a mop on as much area as you want and spread some more every 15 minutes or so.
Mop and Glo is a different animal. It does not dissolve but with enough dwell time it will lift from the surface so you can remove it.
Agree, this is an old topical finish (AKA sealer) such as Mop 'N' Glo or floor finish for VCT. As it gets older and broken down, moisture gets under it causing the white look.
Advice above on how to remove this is correct. Don't expect it to be easy. They made a very poor choice in the sealer for this grout. In the future, use a penetrating or impregnating sealer made for grout. This will fill the crevices, nooks and crannies instead of staying on top.
The only thing I’d add, if this isn’t water base sealer/finish you will have to go down the road of furniture stripper. You will know fairly quickly if it’s water base or not.
Last year I have a mother of a huge church hall that had urethane finish all over. I could have bought shares in the stripper I used. Money was amazing but so was the work. Thank god for stopping brushes.