Discoloration in the parquet, who has an idea?

Hello everyone,
Today we noticed an unusual discoloration in our parquet! It happened overnight. The underfloor heating was off as the place was not yet occupied. The parquet has been laid for at least four months. It would be great if anyone has an idea!
Best regards

That most likely comes from the sun. Was something standing or lying on it?

Hi, No, it is still new and unoccupied and last night we also did not have much sun. So nothing was noticed yesterday. The only difference is that the underfloor heating is off. Otherwise very little sun in the last few days.

It may possibly be older and only noticed now. The defined lines clearly indicate sun rays that did not reach the covered area. It is actually quite typical.

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It is very difficult to make an assessment based on the photos alone, especially since you do not clearly specify which aspect should be focused on.
In photo 1, for example, a diagonal shading can be seen. Is that it?
In photos 2 + 3, I can recognize different (conspicuous) surface textures of darker as well as lighter elements laid adjacent to each other on the surface. Is that it?
Or a kind of whitening of the lively surface, also visible in the aforementioned photos?
As "Mycraft" expressed, I also suspect that changes, however they may be, did not occur “overnight” but rather as a gradual development with an increasing tendency.
In this context, it may also be important which type of floorboard (manufacturer), which wood species, and which surface protection were used, whether this was done at the factory or on site, and whether the boards were glued down or laid loose (floating).
Regards: KlaRa

Hello KlaRa,
I will try to shed some light on the matter. So it’s actually about the shadow-like lines that can be seen on all three pictures. They run relatively straight. Since we only had the handover last Thursday, I am quite sure that this "dark area" was not there before. The parquet is from the company Gunrebe and was glued down. As I said, the only difference is that we have turned off the underfloor heating since it will be unoccupied for another two months.
Thank you very much for the help!
Saludos