I mean, the only variables as far as I can tell are vitamin B deficiency and poor water quality.
If you are giving your plants a full three part fertilizer then they are most likely not vitamin B deficient, at least I've never had that issue but I've also never ran AN. Since you have given almost no information, I'll guess.
If you're in hydro, I'm guessing the water is either too hot or too cold, I'll guess the water is too cold since it's winter. Also if you're in hydro you should have a ppm/ec meter and a ph meter/test kit and use them regularly.
Do you have your light on a timer and not interrupting the night cycle at all?
Were the plants even fully matured?
If air temp is 70-80 degrees, water temps 65-68 degrees, nutrient level is in a good area not too high not too low, you strain is not a tiny yielder, you got good air flow, let plants veg out long enough/or run enough clones to account for lack of veg and you never interrupt the dark cycle. Then I'd say you got some serious bad luck and I would change strains or quit. Not suggesting to give up on growing, but it's not for everyone. I've had several friends see what I do and think it would be a fun idea and they give up relatively quickly. Good luck.