I agree with the others, it's a total myth about the Anubias.
My breeding CRS male moved into my Anubia walled tank all by himself not long after hacking the roots off many Anubias and planting them in the wall, no water changes had been performed up to this point so if the roots were leaking any toxins they would have all still been there when Geronimo arrived. The Anubias are Nana Bonsai variety, some roots have broken off since planting and remain in the tank to break down, there are also torn leaves, one or two made recently when I was chasing down berried cherries to evict, there is also a Coffeefolia in there that was not doing well when bought as it had an open wound, it struggles and has also tried to grow an emerged leaf which died, so if this other type of Anubia leaks toxins they should be in the tank right now.
The shrimp in this tank thrive!
🙂