I can only offer my observations, I don't know why this works but it does for me. I made my own simple hydroponic setup from stuff I bought from the hardware store because I'm growing in a bedroom in my house and any other kind of soil or medium is too messy and hard to deal with.
I cut my own rockwool blocks from slabs to fit my pots. The cuts are rooted in small rockwool cubes then transplanted to the rockwool in the pots for veg. There is nothing else in my pots no clay or anything just the rockwool.
The pump runs 24/7 so the roots are constantly wet even when the light is off and I don't have the problems described here. I'll clarify this and say the roots are always wet but not submerged in water, it's constantly draining. They are also exposed to air. The res also has 2 air pumps so the nutrients contain oxygen as well. The rockwool in the pots stays relatively dry not waterlogged anyway.
I'm certainly not trying to say I'm right just that this has worked consistently for me. Better than the systems I've bought from hydroponics shops anyway.