If it is your winter now, you are in the southern hemisphere Im guessing...are you in south africa, south america, or south australia? your zone says 'SA'.... winter time is the dormant season for most plumeria; try to keep your cuttings warm inside/in a greenhouse and certainly on a heat mat if you have one.

Rooting over the winter months can prove difficult but is not impossible. do not water them at all until they have leaves, if your soil continues to be moist it may induce rot on the cutting so keep a close watch on the lowest part of the stem

if they had large leaves when you planted them and the leaves were not removed, the leaves can drain the cutting through transpiration but the fluid cannot be replaced without adequate roots...leading to dehydration and likely the cause of your cuttings drooping

pictures can speak volumes and may show something you may not know is important..can you post a pic or two?
also, how long have they been rooting? did you callous them before planting? what is your soil medium composed of? temps hi/low inside?