growing on trays

[Zandor]

could it have anything to do with taking cuttings from them?

It could be anything.

I would look more at common and uncommon elements. Your nutrients feed them both so that can't be it. The light is the same so that can't be it. What about air flow? The only difference I can tell from your post is the trays.

There are many different root problems that in NFT tray's spread quickly and easily from one root to the other roots.

Do the roots smell?