We have no issues with cloning the Jackberry, but it is always possible to get a clone that have problems with shooting roots in a 5-10 days period.
We always use clones that will have a fast rooting proces because we are working a lot with clones, so al our parrents that are used are selected to root fast.
some strains just need way more time then others. eventually you have given your mother's too much ferts that can slow down the process of forming roots big time. some strains i had where the badest cloners ever from 10 clones one rooted periode i trashed it because of the bad cloning behavior. I select in the first place for cloning and fast veg+flower time