Looks like a bell curve $3/4$ of the way across. I’m guessing warm air is leaking to the inside, on the bottom, below crest, and also adhering to the edges, preventing temperature gradient needed to allow condensation. But I can’t see anything to confirm this.
Please check if there's more gap in the farthest down-right part of the window, between the glass and threshold.
As the room cools, it lets more air to pass through that passage, and causing a convection current within that small region. This creates a pattern almost like a Gaussian distribution, as in that region, air cannot condense, as its circulating due to convection current in the hot-cold air transition area.