I had a similar experience a couple years back. In my case it was a combination of lack of oxygen in the water with water temps that were too high. I added some additional air stones to the raft tanks and things got instantly better.
I added some air stones today and it seems like the air stones bubbled the coconut coir/vermiculite mix right out of there.
Has anyone else experienced this before?
Guessing ..High Temp water, or planting to deep (as in your plant is under water above the roots), or Ph is to high . Or the outside ait temp is to hot for leafy greens.
What's the best temp for water in rafts?
I'm in Hawaii...
I try to keep my tank at 70F but it fluctuates based on the fish tank temps. Air really helps.