I can confirm all of my lights work as before after the 3.1 update, IE, no issues with lights not illuminating ground anymore.

 

 

My issue is purely the landing and taxi lights do not illuminate the ground at dusk or dawn. Its really difficult to articulate in words and is time dependant in the sim.

 

Perhaps I've seen this problem. Basically, all lights defined by the runway object are missing including approach, edge, vasi and taxi edge.  At the time this happened I had just upgraded the video card driver and when I rolled back to the previous version the problem went away.

 

Try updating your video driver if you have not done so in awhile, or alternatively if you have updated try rolling back to previous version.

 

Our problems may have had same symptoms but different causes but there is no harm in trying this simple solution.