I have had a similar experience before, looks like the plants are starting to fail from taking too long to root. How often are you watering them and when did you start them?
Here is a cheap cloner that actually works, I haven't had a clone fail rooting yet.
Clone King:
https://www.amazon.com/CLONE-KING-Aeroponic-Cloning-Machine/dp/B008NRQJC0
Its simple to use, I add clonex clone nutrients to the reservoir. Not sure if you even have to, you will have roots in a week. Everyone I have turned onto these cloners say they work better than high cost ones. The spray system is way better than other systems, drenching the stems equally.
Frey the sides of the stems that are buried or in the cloner, you will get faster rooting. If you don't do this, the stems often have to rot a little to start rooting and the plant takes damage from taking so long to root. I take scissors or a razor and frey down to the core of the stem and make a diagonal cut when taking the cutting.