I have an absurd plant collection (absurd in that plants are in every room of my house... and I dont meant one or two)!
First and foremost - any plant is susceptible to transplant stress. If you change the soil medium, they may drop leaves. If you don't change soil, but change the light and humidity they were accustomed to, they'll drop leaves. I import a lot of plants, and many of them die or nearly die from the stress... but once they get adjusted to their new location, they will rebound.
Judging by the amount of yellow, dropping leaves on your one plant, I'd suspect that you are overwatering. Rather than cutting back water, I'd recommend repotting them into something that drains better. That's not a bad idea, anyway, as plants from the big box stores almost always are infested with plant pests and snails/slugs. Here's what I like to use:
Mix:
- shredded cocoa fiber (I like Zoomed's brand of Eco Earth cocoa fiber)
- medium and/or coarse horticultural charcoal (not the kind for your grill)
- medium and/or coarse orchid bark (orchiata is great or pine bark (pinus radiata - NOT the bark for mulch)
- perlite (but if used for a chameleon cage, I'd skip perlite and double up the bark/charcoal instead)
Mix those together to get a very chunky soil mix. The chunks of charcoal and bark create air pockets and help with drainage. You can even add more soil amendments, but this is a good start for good drainage. Avoid perlite as it will be ingested (even the bigger pieces) and is harmful. I also add a drainage layer... the LECA mentioned above is a good drainage layer. I hate using that stuff for anything other than drainage (some people use it in place of soil... and it sucks)
If its a male's cage, I would just sprinkle 2" of shredded cocoa fiber on top so that there's no chance they'll try to eat the bark chunks (but you should also being using larger chunks to make them more likely to spit it out if they snag a piece). For females, I may only use the bigger chunks and add more cocoa fiber strands (long and hairy like) to make it a bit better drainage. The reason being is that the girls kick up so much soil when digging that they'll quickly bring all the bark to the surface. They're also always starving, so they are more likely to try to eat the medium pieces.
Also - wash your plants really well with a mix of water and dawn dishsoap (I also add 1-2 TB of isopropyl alcohol) in a spray bottle, and then after soaking for 5 mins, rinse really well. Sometimes I repeat this 2x. That will help remove some of plant pests, fungicides, pesticides, and fertilizers they spray.
Last but not least - make srue you have adequate light. More light = more watering and humidity needs. Less light = less watering. A Jungle Dawn is probably sufficient in that size enclosure.
. My girlfriend and I thought we were maybe cooking it because the one pothos halfway down the cage has never had issues 
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