Joints in the bathroom: joint material on the cleaning cloth and coating on the joints

Hello,
I have two questions about grout in the bathroom. We built three years ago and therefore have a fairly new bathroom.
Now, over time, two things have become noticeable:

1. In the attached pictures you can see that something has been deposited on the grout. This is in one spot in the bathroom, in the shower, the last two rows of tiles below the ceiling. We hadn't noticed this before. I have no idea what this could be or if this is normal. Could someone tell me what it might be?

2. While cleaning, we have noticed for a while now that the cleaning cloth becomes slightly whitish/gray. It seems that we are removing grout material while cleaning. Until now, we thought it would stop over time, but it has been happening for so long that we are starting to doubt that. We use water and bathroom cleaner for cleaning. Is this normal or could it be a concern that the grout material is simply too easily soluble?

Thank you
Sven

Remote diagnosis is always difficult, but it does indeed look like the joint mortar is dissolving. After 3 years, there should no longer be a light film. Basically, repair the joints! If there is no longer any warranty, scrape out the joints (or use a small angle grinder) and re-grout. There are also repair systems available at the hardware store.