Is it just one window, or a few of them all in the same location?
If it’s a single window and the others around it are not affected, then yes, there could be a faulty seal.
If there’s fogging or condensation occurring between the panes of glass (you can see it, but you can’t touch it), then yes, there’s definitely something wrong. Contact the supplier.
If a few windows are fogging up or condensation is forming on the internal surface (the side of the glass you can touch), then it might just be a temperature and ventilation issue inside your home.
Double glazing is not perfect. Some basic versions sold in New Zealand (non-thermally broken frames, aluminium spacing and standard glass) are barely better than good single glazed, timber framed windows. If it’s cold enough and the relative humidity is high enough inside the home, condensation will still form on the internal surface.
On cold days our double glazing has early morning condensation forming on the OUTSIDE!
I take that to be a sign of a well performing house.
My interpretation of the science is that the outside face of the outside pane gradually cools down to the pre-dawn air temperature as the insulating performance of the windows doesn’t allow the inside heat of the house to warm out the outside glass. Then when the sun comes up the outside air temperature rises quicker than the surface temperature of the glass. As the air temperature rises, so does it’s moisture carrying capacity (moisture from the garden, rising from the ground, etc). This increased moisture in the air then condenses out on the still cold outside face of the glass, until such time as the outside air temperature has gradually warmed the glass up and when it’s above dew point, the condensation evaporates again.