Random and noise modifiers can also cause flipping and mesh breakage. // That was it for the leafs thank you
For the mesh disappearing when < parent, you could try setting a minimum diameter. // The branch mesh isn't disappearing, but the width of the branch was its original size given in directional modifiers and didn't respect the "< parent" option, because it was at 100% in "PathPosDistr". Putting it to 99% fixed it, might have something to do with the "0" size you were mentioning.
Thanks for the feedback, the leaves are fixed