The water level is much too high, you should have lids for the bucket, and cut out a hole for whatever size net pots. And then the level should be roughly 1/2 to an inch below the bottom of the net pot. Well below the stalk of the plant at the least.
Plenty of times I've had plants grow to big, and the net pot pop through the hole into the res. A few times won't hurt if caught in time, but left for long periods of time is like dampening off on a hydro plant. Either choke it out or it will rot.
If you tug on some of the roots I bet they will be mushy, even if they look ok, and just pull away from the root ball in clumps.
Actually.. It appears that your system is designed with the overflows up toward the top, i'm guessing the easiest option would be to buy new buckets and make the overflows lower. Unless you can figure out a way to raise the plants up from now on.