Looking at the first picture again..where those leaves planted without the vine stem?
It seems the remaining green ones are still attached to some stem. Is that stem the ones with roots?
Maybe it needs the vine stem with the leaves to form the roots, otherwise the leaf alone will just rot if stuck in the media. Or if you really want to root the leaf alone, maybe do like we usually do with the other types of succulents, lay it on the soil and keep warm till roots come out.
