Joints of the tiled floor too soft?!

Hello dear forum members,

about 2 months after moving into our new build, we noticed that the joints in almost the entire tiled floor area are too soft. You can scrape them out with your fingernail or, for example, with a scrub brush if you brush back and forth a few times. Of course, we informed the tiler about this; an appointment with the grout manufacturer will take place soon. So far so good/bad. The mortar company informed me by phone in advance that this could "most likely" be fixed with a hardener (OH 100).

Does anyone of you have experience with this? Should we rather insist on re-grouting?

Thank you in advance Fugophob :-)

If you use a pressure washer on joints that you can scrub away with a brush, will there be anything left of the joint?

Correct, with a high-pressure cleaner nothing is left. We are talking about the floor INSIDE the house. Meanwhile, the appointment took place; as suspected, they want to work with a hardener. However, the risk of incorrect application is too high for me (graying in natural stone, etc.). After consulting with a lawyer, one unfortunately has to accept the type of rework (unless it is doomed to fail from the start, which is not the case). So either take the risk or regrouting at your own expense. Great...