Grout starting to crack around floor tiles

[rl11tr]

You need a mastic joint matching grout colour around the floor to wall junction.
Should always have all tile to tile junctions siliconed anyway, as regardless of what they are fixed to, the grout always cracks and falls out as it’s not flexible

Yes; floor to wall junction is siliconed and not a problem - there is only about 1m of floor to wall anyway

 

[rl11tr]

Thanks for all of the help

Thought I'd put up a photo to show what it looks like. The whole tiled area is only 2m x 1m. It's really just used as a cloakroom but happens to have a bath with shower over, in the room too. The hairline cracks are really hairline - wife can't see them but they are definitely there and there is the tiniest movement up and down if I press a couple of the tile corners. Cracks are only across the 1m width too. I'm thinking best to leave for now but take up tiles when they do come loose and screw down chipboard into concrete floor underneath. Then use more flexible adhesive and grout. I think I'd have probably been OK if I'd gone for S2 and a flexible grout in the first place. The Ultra Tile Fix ProFlex SPES S1 supplied seems to be like concrete with zero flex and the Mapei UltraColor-Plus grout doesn't mention being flexible at all.

 

[Jon591]

Yes; floor to wall junction is siliconed and not a problem - there is only about 1m of floor to wall anyway

Ah sorry I misread the original post and assumed as it usually is that the crack was around the perimeter,
The tiler should have used a flexible adhesive and grout if not you will have this problem. If the tiler did follow correct instructions then as suggested your sub floor is the issue, and with that I can’t give a helpful suggestion