Ok. That makes more sense.
If I understand it correctly, your skimmer was off overnight. Now the water level inside the skimmer body has dropped.
Leaving the skimmer off overnight would have allowed time for the water to dissolve any salt creep buildup in the skimmer's venturi inlet. In turn, it would allow the skimmer to pull in more air. I used to have to clean the inlet to my old ASM'S Sedra pump from time to time. I would always have to readjust to raise the water level afterwards.
Could be something as simple as that if I'm understanding the problem correctly.