Today in -15 C degrees I noticed that several windows have condensation on the inside in the lower corners, despite the low humidity inside 40%.
The windows are aluminum and wood with triple glazing with a warm edge. I am surprised that only 4 of the 20 windows are affected. Personally, I have also found that if you almost stick your finger in the corner, you can see cold air through the seal.
Is this a defect or is it inevitable and acceptable given the outdoor temperatures?
The window definitely remains the coldest part of the (modern) wall, doesn't it? If there's also high humidity in the room.
Even with triple glazing at a temperature difference of 35 C (-15 outside, +20 inside) physics cannot be outsmarted.
If it's very cold outside, condensation can form. If the room is not heated in addition, the probability of condensation increases. The dew point shifts.