(Let me precursor this with the fact that I have been searching both forums and while there is great information, omg is there a lot of information in a bunch of random places and about different pieces of this.  Im hoping someone may be willing to answer this specific question so I know im going down the right path.)

I have a bunch of cuttings that I rooted and weened off of humidity and are currently under some 6500k lights.  About 20% of them are having this problem... They are all 5-8" tall they all had a few smaller leaves, that were green and growing.  They are now wilted and dropping those leaves.  They have been out of humidity long enough that I dont think its a readjustment thing.  I water them with maybe 1/4-1/2 a cup of water every 3 days.  I dont think its over watering as the 1 gallon pots get pretty dry in between waterings and they never actually get fully saturated (should they)?  The lights are on for 14-16 hours a day, they are in about 82 degrees and 54% humidity.  I do have some fungus gnats but it doesnt seem to be a huge infestation and have a lot of these that are 100% happy and growing.  The other thing I did do was put in 1/4 teaspoon of worm castings into each pot a few weeks ago.

What could the problem be? Would it be the fertilizer? Would it be not enough water? Would it be not enough light or too much light?  These are in mostly Promix HP.  I have ones in my own mix and MG mix that are doing fine on the same rack.  Are they just weak cuttings in the first place? Is it worth trying to save them? 

Thank you in advance.  Here is a photo of some of them.

 

Could be the lights are too low scorching leaves...or that the potting soil haste much fertilizer in them.. or maybe the soil is to compacted?  I might try raise the lights, add a small fan to move the air a bit, and try watering from below (dunk them briefly in 3-4" bin of water -about half way up the pot-- and let drain off. That should last 4 + days). If soil is too compact you can gently squeeze the sides of the pots to break it up a bit--just be careful not to break off roots--but compact soil will create pockets of mucky dampness in the pots that could result in rot).  I would also say never underestimate the damage gnats can do. There's a product called gnatrol you can add to you water to help alleviate gnat. If you are using the bottom water method you can add it to your bin of water before you dunk your pots. 

Good luck

How do you know the condition of the roots? I have seen (many times) a cutting with a lot of leaf growth yet little if any roots.
What is the percentage of perlite in your soil mix? I use 75%.
What is the temperature at the leaves? Bright lights can dry out and burn leaves quickly.
What do you consider your "gnat load"? As soon as I see 1 &^*^%#@ gnat I add gnatrol, nematodes and yellow sticky paper.
Do you spray your cuttings with water?

Recomer has some good suggestions. 

Here is a few other things you may want to try;

From the photos I don't think your lights are an issue since many of the plants look OK and I can't see any burn damage on the leaves.  Look for burn marks on leaves or test by putting your hand where the top of plant is. if it feels hot or you see sunburn on leaves then raise the lights a bit.

Fertilizer is great but I am sure I have killed some plants by burning the roots with too strong a feeding. 
Whatever the label says use much less (1/3) of label recommendation is fine for young rooted cuttings.  Water them with just water before feeding them.

The yellowing leaves could indicate overwatering. 
This is consistent with the leaves wilting due to the roots rotting.  Before watering check the soil moisture deep down in the pot.  Bring up some soil and see if it is wet or cut a hole in the side of pot to look.  If the mix stays wet it will rot the young roots and stem.

I would re-pot some of the problem ones and check the roots and stem for rot.  Re-pot in pre dampened soil not wet soil. 
If you don't want to repot do what recomer said or stick newspaper/paper towels in the drainage holes to wick away the water.


 

- How do you know the condition of the roots? I have seen (many times) a cutting with a lot of leaf growth yet little if any roots.
I obviously do not have xray vision so short of uprooting them I can just tell you they were rooted in other smaller pots and upotted when the roots looked good enough to up pot.  Again I have 150 cuttings and theres about 20 of them that are having these issues. So what ive been doing has been working on almost 90% of them.  

- What is the percentage of perlite in your soil mix? I use 75%.
Both HP Promix and the mix i was making have much less than 75% perlite and the other cuttings that are doing fine are also in this mix.  So I dont know if that is the issue but I guess it could be.  Although im willing to bet in a 75% perlite mix, bottom watering wouldnt work like the other poster said since no water would really be retained or soaked up.

- What is the temperature at the leaves? Bright lights can dry out and burn leaves quickly.
This is a possible issue and one im wondering about but again all the "happy" ones are sitting on the same rack as the "sad" ones.  So its tough to blame the light in my mind.  Temp of leaves is between 82-85 on average, I just checked 10 of them.

- What do you consider your "gnat load"? As soon as I see 1 &^*^%#@ gnat I add gnatrol, nematodes and yellow sticky paper.
I dont have a ratio to go by but I will tell you that I can see some flying around.  With that said I was told they only really bother dying plant material so if the plants were healthy they shouldnt be the issue but they very well could be. I will pick up some gnat control and go with it.

- Do you spray your cuttings with water? 
I did originally when they were weaning off but no I have no in the past 3 weeks as there has been no need to and I didnt want to risk burning the leaves by doing it.

3 days is way too often until they have more leaves and 1/4 c. is not even close to enough, I don't measure but it must take at least a pint if you are letting it drain out the bottom. You should be judging the weight of your containers, water enough to make them heavy and not again until they are lite. The wilted ones are probably toast, when the leaves dry up without dropping it means the stem is dead, a live growth will drop the leaf if it needs to. Do an investigation, my guess is you have wet and dry spots in the mix.

This is a pic of some on the next rack down.  A few are further into the growth state and some started life as larger cuttings.  Also this is my first go at this so I swapped mix a couple times / used what I had.. next time I will stick with 1 type so its easier to manage and know whats going on.


 

Louneo, I found good info on what may possibly be happening to your cuttings AND, how to help them! I hope you find the solution here...
http://www.smallfootprintfamily.com/controlling-fungus-gnats-organically

   A good Soil Moisture Meter is on sale at Amazon right now for $8. 

http://www.amazon.com/Etekcity-Indoor-Outdoor-Moisture-Hygrometer/dp/B00CTPXXEE/ref=pd_sim_86_2?ie=UTF8&dpID=51hrNE1rrYL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=0FGB24JZR1BDFN6FEK55
   

   By comparing the readings of the soil from the happy occupants vs. that of the struggling ones, you will quickly see if the level of moisture might be a contributing factor.

   Blue

Just because I truly need one, its on its way, I just ordered that meter.  I just think the ones that are hanging on just had a stronger root system. I will work on the watering problem starting tomorrow.  Thank you guys, I truly thing that is the issue.  All of the mix is not getting equal watering, this is 100% true.

I would not mess with bare rooting them. That will surely be the nail in th coffin. Pull the dead leaves off. As long as the green tip and branch are not wilting you are fine. When you transitioned them out of the humidity the problem probably happened. It takes days to weeks for the leaves to show damage. Some probably needed to be weened out of the humidity longer. There roots were probably not as developed.
Cian