At a first glance it looks like transpiration. When the humidity is to high, the transpiration can't evaporate. But I have only observed that when plants are to close and the transpiration from the underside of one leaf condense on the upperside of the leaf next to it. But when I take a closer your pictures it looks like the plant is bleeding through cracks in the stem. I agree, that's strange.
If the stems and veins of the leaves is in bad condition, I would calibrate the PH-meter and then check the PH in the nutrient solution as well as the run off. It might be a nutrient lockout. I killed a whole grow room once when I got lazy and didn't calibrate the PH-meter. The disaster started with dead veins and weird colorations on stems and curling. I can't tell for sure from the pictures, but it looks like one leave is twisting upside down in the second picture.
Please update this thread when you have solved the mystery with the oozing stems.