Cracked tiles

They’ll unfortunately need to be replaced as nothing will be strong enough to bring it back to the original strength. If they’ve cracked it also means there’s something wrong with the adhesive underneath i.e not enough

Hardest bit is getting matching replacements if you don’t have spares. The hole underneath suggests the tiles were put onto blobs of adhesive rather than a ridged ‘carpet’ of adhesive. If you hear hollow sounds when you tap random areas that will confirm it was a sub-standard tiling job.