Hello. I think the main reason the clones fail is Pythium Root Rot Fungus. It's common in most fresh water around the world. It's in the municipal drinking water. Chlorine doesn't kill it. So I suggest you use filtered, boiled or distilled water to make your clones with. I made 21 clones about 3 weeks ago and 2 died.
Soak your medium with seaweed, 10 ml/G to help stress recovery and water uptake. Use as foliar spray on the little clones.
Leaving too many leaves on the stock so the little cutting is struggling to transpire (breath).
These are the main reasons , in my opinion, why clones fail.
Chuck.
I'd complain if I got a rude answer, like the one below.