If the both are in the same pot and you haven't added any fertilizers it is hard to say.
When trying to root cuttings the newly created roots are very sensitive.
It could be they don't like something in the soil and one of them is just showing the signs earlier.
What soil are you using?
Plants from Amazonas region tend to like slightly acidic soil but im no expert on Caapi.
Have you added something in the soil who make it alkaline as garden lime or similar?
I don't think that would be good.
Also if you have the small flies, gnats, in the soil, the larvees can hurt the newly developed roots.
Hopefully someone expert on Caapi can help out.
If the other one also starts to look as it is going the same way, i would try put them in new soil.
I use citrus soil (ph 5-5.5) for amazonian plants as Psychotria but im not sure about what Caapi likes.
You could remove them from the soil and try rooting them in moist perlite instead.
Then you would know there isn't anything in the soil that can affect them.
But they maybe have roots already?
To put them in a cup of moist perlite and put a plastic bag around usually works good for developing roots, or if you have a hydroponic rooter thingy.
I have built a "rooter thingy" by putting a large airstone in a small plastic tub, filled with water + 10 drops of cloonex rooting hormone.
Then i connect a aquarium airpump to the airstone.
The cuttings are placed so the bottom end is about 2cm above the water level.
I get really good roots in this one.
I have just rooted something that might be Caapi in it.
I snatched the cutting at a botanical garden so im not sure what it is, but it looks like Caapi.
Can you give little more info?
Good luck, i hope it get helthier soon.
Grower
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