I have been have a problem with a significant portion of my new cuttings.  I get everything to root just fine, but once I transfer them to soil several die off.  First the leaves go limp, then dry up, then the roots die off.

Could too much humidity cause this?

The same problem happened to me before. I doubt that its root was too deep in big pot and got temp lower than small cup.

What I learned, HERE.

I have the same problem, I lost ALOT!!!! about 75%. I thought maybe I was starting to much at once.

i use MG perlite for cuttings in cup and 1 gal. once moved to bigger pots, i change to different perlite. last year, i had rather good results. most of the cuttings that has gone into the cup then into the 1 gal all survived. 

this year, i lost one after going into the 1 gal. well.. two. that's counting 1 Persian White that i didn't pay too much attention to humidity. good thing i had duplicate of PW and it survived. 

one thing i keep noticing is that even the same batch of soil mix will have different drain rate depending on which container it's in. but most of the time, the cuttings that goes into the 1 gal after the cup seems to have good enough roots to handle some wet feet. even with fine grade perlite, i don't see much problem. i usually mix them with seedling soil before wetting the mix and once again after i wet them with water. make sure the perlite is evenly distributed before using it in the container. 

the one that died after doing well in the cup, i'm not sure what happened to it. the leaves were very large and i don't remember why, but i cut all of them off. and i left it in the partial sun to put out new leaves. after a week or two, the branch which had that leaves started drying up. i guess it's a goner. still in the pot, but i need to remove it to reuse the pot. 

i cup off leaves from Col de Dame Noir also, but that one i left one leaf on. that one is actually doing great. maybe i should have left at least one leaf on. 

i always keep duplicate of the cuttings i consider precious. i have good duplicate that is doing very well for this one. 

I had one big disappointment this year that happened the same way. But I guess if you didn't have some failures, the successes wouldn't be as much fun.