Hairline cracks in bathroom floor tile grout

The crew supposedly fixed the issue twice, last time in early June. Is this worth throwing a hissy fit about? The tiles do not appear to be loose, but I'm concerned that they will become so or water damage.

Cracks in the grout are generally the result of movement of the substrate. The only actual grout failure is the result of an improperly mixed grout. Too wet or too dry, it could crack as it dries, but that usually starts to show itself within days of the installtion. If the cracks appear later, then its movement ubder the tile, causing stress in the grout and eventually, cracking. Another possibility is having use sanded grout where unsanded should have been used, or vice versa, In general, unsanded grout is used for joints up to 1/8"; sanded grout for joints over 1/8".

If that's the case, the fix is to stabalize the the substrate. Maybe that can be done from below. but it might be necessary to - I hate to say it - remove the tile and start again on a newly stabalized base.

As to 'blame' ...... did the tiler say he would check the base and pronounce it fit? Did you say/imply it was fit? Did this even get addressed.

This can turn into one of those cases where no one will accept blame.

A semi-sorta fix, by the way is to remove the grout and replace it with a color matched sanded caulk. That looks like grout and flexes enough not to crack. But it needs periodic replacement since it won't last as long as grout.

They replaced the subfloor. They've been back twice to fix the cracks in the grout. The last time I insisted they take the old grout old and redo. Though I wasn't here, so I have no confirmation that they did it.