What leaps out at me is the rockwool...the stuff used to raise aquarium plants in large numbers and what is wrapped around the rootstock/bulb etc before the plant is put into one of those plastic pot thingies....or the ceramic collar that is also used for smaller and more delicate plants when on sale at the shop.
In the shop there is very little flow from filters, no fish buzzing about etc, so the rockwool stays neatly inside the pot or collar. And they are packed into their plant only aquariums very very tightly, so little or no movement.
Once the plants are placed into an aquarium and have some space to stretch themselves out, and there is a reasonable flow from the filters brushing over them and the fish get nosy and start snuffling and digging in them....the rockwool breaks down.
Filaments of rockwool are microscopic but they can and do lodge in the mouths and gills of the fish over a fairly short time, they are free floating in the water and every breath a fish takes, every snuffle and every feed, those filaments are entering the fish.....eventually making the fish very unwell and then death follows. Filaments clog the mouth, throat, gills and digestive system.
It is why it is always advised to remove plants from their pots and the rockwool before placing them into an aquarium