Transparent objects don’t write to the depth buffer and they are only sorted from back to front before being rendered. As you have only 4 big objects for your foliages and they are one over the other, sometimes the ordering of those objects change when the camera moves/rotates because the depth used for the sorting is the center of the bounding sphere.
To correct the problem in your case, for all 4 materials you should:
- enable the “Need depth pre-pass” option
- change the transparency mode from “Alpha Blend” to “Alpha blend and test”
With those changes, it does work for me.