Are you slicing the cutting up the stem a good inch and cake rooting gel/powder on it? I'm new to cloning but I've been successful cloning three strains my friend couldn't. About the only thing different I did then him was slice the stem up the middle a good inch, I used Clonex he used Olivias, I used light warrior soil he uses cubes, I used FF big bloom and Route 66 to both spray leaves and water soil. Other then those things I can't think of much. We both use basic trays with domes and spray to keep RH 90% or so, both of us us T5 lights. We both take cuttings from bottom. The strains were Le Fruit Defendu, White Queen and a unknown. Maybe try to cut softer stem/branched cuttings. I guess I will eventually come across a fussy strain. btw, what strain are you trying to clone?