When you driving at night with AC on, windscreen will get cold. if it is much cooler than the outside atmosphere, mist will be concentrate on outside of the windscreen. Same as when you pour cold water into a glass, mist will be on the outside of the glass.
The solution would be to heat up the windscreen and mist will disappear. I am regularly facing this problem while driving at night. My solution is to increase the temperature from AC temperature controller and put the air flow into the windscreen. Not for long , about a minute . Then the mist will be gone. But it again comes on after an hour or so. A proper adjustment of temperature inside the car should keep out this problem. But honestly I haven't been able to find that adjustment for myself yet. LOL.