Water has formed between the window panes

Good day,

Today, after it was about minus 3 degrees overnight, we noticed that water had formed between the window panes.

The window fitter says that this is not a defect. However, he could not explain why this happens...

What do you think about this?
Thank you.

that water has formed between the window panes.

Formed - well, I would say that moisture has probably condensed into droplets.

The window installer says that this is not a defect. However, he was also unable to explain why this happens ...

But he should, if he claims that it is not a defect. I suspect a tiny leak in the seal of the pane unit. Then the gas exchanges with the surrounding air with all its components. I don’t see this going away on its own.

I agree with the words of 11ant:

A noble gas is inserted between the panes for insulation. If this is not sufficiently sealed, it can mix with more humid ambient air. This then condenses on the glass at low temperatures.

We had this several times in our rental apartment. In contrast to the windows without moisture inside, the affected ones were noticeably cooler in the colder months.

It was reported to the landlord as a defect and replaced every time...