From everything I can see in your diary the debris and the pH swings are coming from the same two things the plant with the huge root mass is shedding root hairs whenever it gets lifted or shifted even a little and the EC keeps rising because the plant is drinking water faster than nutrients. That combination makes the outer root layer flake off and fall into the water and it also makes the pH move around a lot.
Nothing you described looks like rot, no slime, no smell, no mushy roots, and the plant itself still looks healthy. The roots are just reacting to stress and the pH drift is just the reservoir concentrating overnight. Even if you don’t lift the roots often a very large root ball will still shed when it gets moved at all and yours is much bigger than the other plant’s. That’s why one has debris and the other doesn’t The fix is just keeping things stable avoiding unnecessary root movement and letting the plant settle without constantly pulling it out. The issue is mechanical shedding and nutrient concentration drift not disease. Happy growing growmie 👊👍