Cracks in the tile joints in the shower

I can contribute a solid experience on this. We had our bathroom tiled by a tiler, with properly sealed drywall behind the shower. Multi-layered, vibration-free substrate (old building). The shower was installed by a sanitary specialist company. After 3 years, I went to shower, left the house, came back, and one floor below, directly under the shower, there was water on the stair landing. The sanitary company came, puzzled, the drain was said to be tight. Nevertheless, it was sealed again as well as possible, just to be safe. The issue with the shower and moisture repeated, the sanitary company was at a loss. On the second visit, the man actually crawled into the shower and found a hairline crack in the tile on the wall, originating from a drill hole for the shower partition. So a small crack had formed there, and over time, due to the movement of the sliding shower door, a hairline crack developed, through which water had been running behind the wall for who knows how long, until the drywall eventually softened and the water passed through several floor layers, reaching one floor below and then dripping from the ceiling.

Solution: We removed the shower wall, the tiler came, removed the damaged tile, after a drying period behind it renewed the sealing and the drywall, then a new tile was installed. He was there 3 times in total because of this. In the end, we did not drill the shower wall again at that spot but glued it.
One floor below, we opened the ceiling as much as possible, let it dry for 3 weeks, and then closed it again. Thanks to a lot of own effort, we ended up with "only" about 200-250€ in costs.

Conclusion: Huge effort, always two construction sites in the house again, and the worry that it could mold (wood beam ceilings). Costs that, of course, we were stuck with. Ergo: Even with such small damages, there is no joking around when water is involved.

I had the tiler here just now. The problem is apparently that the joint works due to moisture and the drying process. He laid the tiles closely together so that there is little material to work with. By now, he would lay them a bit further apart again. Allegedly, you can't damage anything in the drywall construction or the sealing, since the tile adhesive is still behind it.

We had the same problem on the floor. The joint material came loose. I reported it to Schwörerhaus, since it is within the 5 years. In the meantime, I repaired it myself because we use the shower daily. Schwörerhaus replied after 3-4 days that the joint material is exposed to soap and cleaning agents and would naturally give way, and that it is not a warranty case. But as long as the sealing underneath is not damaged, there is no danger. Well, let’s see.

I had the tiler here now. The problem is probably that the joint moves due to moisture and the drying process. He laid the tiles closely together, so there is little material to work with. Nowadays, he would lay them slightly further apart again.
They say you can't damage the drywall or the sealing because the tile adhesive is still behind it.

Unfortunately, I cannot confirm that. I was there when the tiler removed the tile; definitely, there was enough adhesive on it, spread evenly. The damage still occurred over the course of the 3 years.

It was not about the adhesive, but about the narrowness of the joints. In the tile studio, the tiles are always placed very close together. It obviously looks cool, closely laid tiles with little grout. But in everyday life, it has the disadvantage that there is not enough material to bond. I am supposed to remove the material with the cutter and he will come by and redo the joint. I just had the concern that I might damage the substrate while removing it. However, that would not be a problem due to the adhesive, since the cutter knife does not go through the adhesive.

That's right! Good luck! Better to act now.