It's a messy DIY job, and you may end up breaking at least one tile; but you need to see what's going on under those tiles.
There are grout tools to remove existing grout and lift a tile intact that could allow you to view the sub floor to confirm the underlying issue.
Once you have eyes on the sub floor, the extent and cause of necessary repairs will help you make up your mind.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.