Hardwood floor fillings coming out

I rent this apartment for about this 2 years. The floor has a hardwood that is not treated with any protection layer, like wax or some other finishing as far as I know. I also have floor heating, although my apartment is hot enough and I have it disabled at all times.

I’ve noticed some cracks and I started freaking out with every minor crack that seems to be developing.

For floor mopping I use a Dreame robot, which barely wets the surface. The humidity in the apartment is around 35-55%. Sometimes during wet periods it could of course go much higher. However, I feel that it is much more towards being dry than "wet" anyhow.

It seems that the cracks or things that are coming out from the floor are actually fillings and no the wood itself. The texture of the material is different, the color is much darker and it is coming out as a whole.

Has anyoned faced a similiar situation/has experience with it? I would be interested to know if this is a "serious" damage that I should be worried, if I should clarify with the hausverwaltung to evaluate if it needs maintenance? From what I read this floor requires maintenance every 10 years and that it has a lifespan of 40.

Any input/information/experience would be highly appreciated.

PS: in one of the images you see the bit that was loose. The other bit was probably sucked by the robot.