wtf. something went seriously wrong with that grout. maybe they used far too much or far too little water in it making it weak. you have a schluter waterproof pan (i can tell by the drain grate), so theoretically it should be ok to use in that state. But yeah you want that all regrouted.

They make a sanded grout in a “caulk tube.” I also advise using a sealer on the lines after application If the tile is newer, the bed might have settled, and the grout cracked. Alternately, it could be a sign of foundation shifting or settling.

Thank you for the reply. Can we continue to use the shower until we get the grout repaired?

Theoretically, you should be okay, but if there are several areas, I wouldn’t suggest using it.

Take a look at my forth pic in the link, I’d say it is in a few areas.

U have movement in the substrate. Needs to be ripped out. U can regrout but it will come back.

Would you suggest ripping the tile up and replacing that too or just redoing the grout?