DeleteFace throwing NullReferenceException error on iOS build

As per the subject I am getting an error with DeleteFace(face). Works fin in editor not on iOS build.

Unity vers:
2018.3.11f1

ProBuilder:
4.1.0 (package manager)

Interestingly DeleteFaces(faces) works fine on both editor and device.

Script stripping is unticked (off) in preferences
Have removed and reinstalled probuilder

Appreciate any help.

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object.
2.   at UnityEngine.ProBuilder.SharedVertex.GetSharedVertexLookup (System.Collections.Generic.IList`1[T] sharedVertices, System.Collections.Generic.Dictionary`2[TKey,TValue] lookup) [0x00000] in <00000000000000000000000000000000>:0
3.   at UnityEngine.ProBuilder.ProBuilderMesh.get_sharedVertexLookup () [0x00000] in <00000000000000000000000000000000>:0
4.   at UnityEngine.ProBuilder.MeshOperations.DeleteElements.DeleteFaces (UnityEngine.ProBuilder.ProBuilderMesh mesh, System.Collections.Generic.IList`1[T] faceIndexes) [0x00000] in <00000000000000000000000000000000>:0
5.   at UnityEngine.ProBuilder.MeshOperations.DeleteElements.DeleteFaces (UnityEngine.ProBuilder.ProBuilderMesh mesh, System.Collections.Generic.IEnumerable`1[T] faces) [0x00000] in <00000000000000000000000000000000>:0
6.   at UnityEngine.ProBuilder.MeshOperations.DeleteElements.DeleteFace (UnityEngine.ProBuilder.ProBuilderMesh mesh, UnityEngine.ProBuilder.Face face) [0x00000] in <00000000000000000000000000000000>:0
7.   at SliderController.Start () [0x00000] in <00000000000000000000000000000000>:0
8.