okay i ran it and it's bringing up divide by zero errors so I've aborted before it gets chance to hang.

DivideByZeroException: Division by zero
System.Decimal.Divide (Decimal d1, Decimal d2) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Decimal.cs:626)
System.Decimal.op_Division (Decimal d1, Decimal d2) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Decimal.cs:316)
_LushLODTreeConverter+c__Iterator4.MoveNext () (at Assets/LushLOD Trees/Scripts/_LushLODTreeConverter.cs:2209)
UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)
UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
c__Iterator1:MoveNext() (at Assets/LushLOD Trees/Scripts/_LushLODTreeConverter.cs:1060)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr)

I'm using 2017.1
I'm trying something though. my leaves were originally using the fast shader. I changed them all to the normal shader, but it's possible they hadn't properly updated. I'm just about to try the tree converter again ( after properly reimportig the trees and rebuilding the materials) to see if it does the same thing. 

okay i've fixed my original trees, but I've discovered this square shadow thing is even worse. when i play the scene, it shows ALL the billboards, in white, and with a weird dithering effect on them.