I would start with a double-check of all the basics,
The levels I state below are "just a guideline" that I use for myself, in DWC only, and I wouldn't expect any adverse symptoms, such as the photos you've shown, if I keep within these ranges.
Environment: light height/intensity, temperature, 24 degrees C - 28 degrees C, humidity, 50%-60%, air intake/exhaust sufficiency, no fans blowing too hard or directly on the plant
Nutrients: pH (5.5-6.2), EC (1.2-1.6 in veg), airstone/pump functioning correctly, airspace between net pot and nutrient level, etc.
root health; colour, slime/pythium, insect larvae within the root ball, etc
One more thing I recently learned the hard way is the compatibility of nutrients. Try not to mix different brands, and try not to use too many additives, as it can make things a bit more complicated,
Stick with the basics.
I'm interested as to what might be causing this myself, so please let us know what you discover.
Cheers.