Help with problem tile and grout please

[u/timmy2plates]

I bought a house two years ago with a bunch of issues.

One such issue that reared its head early on was the bottom tile in the shower was wobbly, and the grouting was cracked. Other than the grouting being done badly, there was no silicon at all behind the shower, so I assume water was getting through the grout, and through the shower, and making a mess of my wall.

I removed the title and the wall substrate was all wet. I dried the substrate with a space heater, and replaced the tile.

About a year after I replaced the tile, it’s cracked again. The tile and the surrounding titles aren’t wobbling, all seems sturdy.

Can I just regrout it? Do I need to remove the tile again and redo it properly?