so soon. Could your foundation be shifting a bit to break the grout lines? Sometimes if the floor and walls move a bit it might be recommended to use a good quality 100% silicon on the wall floor intersections. This will allow for slight movement and keep the water out. But, I would check this periodically to make sure the seal is set, when the movement seems to stop, then remove that grout and re grout, then silicon again on top of that.
But, on second thought I would go ahead and take out that grout and re grout following the instructions carefully concerning curring time. then after that do the silicon sealing.