Oof, catastrophic failure. I’m guessing you’re going to find very thin material without adequate backing and a honeycomb support pattern underneath, not some kind of mosaic or whatever you’re imagining. Every one of these tiles is failing and those cracks are exposing their structural shape. The mortar bed below is probably too chintzy and the tiles were not properly bedded to infill the cavity voids. I’m no tile guy. Just a designer who grew up in the trades as a cabinetmaker. I can definitely see that my theory could be wrong but I’m reading this as telegraphing through the tiles. Also, tiles are not constructed in the way you’re describing. One other option could be they did an incompetent grouting job on actual hexagonal tiles laid up on a common substrate. Those are pre laid up squares with grout gaps between the hexagons. If they filled the grout flush with the top, this could be the grout exposing that failed install. Might be possible to re-grout but I seriously doubt a tile sub would go for it. They’d probably rip this out and do it correctly. No sub wants the liability of shoddy work coming back on them. It might have been remuddling on behalf of unqualified previous owners, which is more likely than a pro doing this. Anyhow, cracks telegraphing through are indicative of unstable substrate/backer. Should never happen.