When "Weld Distance" is set to 2 or higher and "Weld Vertices" button is selected from Options window, it causes the editor to throw below error:
"[Physics.PhysX] TriangleMesh::loadFromDesc: desc.isValid() failed!
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)"
Refer attached video.

Steps to repro:
1. Create a new project.
2. Window > Package Manager > ProBuilder(4.3.0-preview.9) > Install
3. Tools > ProBuilder > ProBuilder Window
4. Create a new shape
5. Select "Vertex Selection" tool in scene view
6. Drag mouse to select all the vertices on the Cube
7. Open "Weld Vertice" option window
8. Set Wel Distance to 2 and select "Wel Vertices"

Actual Result:
"[Physics.PhysX] TriangleMesh::loadFromDesc: desc.isValid() failed!" error is thrown on selecting "Weld Vertices" tool

Expected Result:
Vertice should be weld without throwing any exception in the console

Occurring in:
2020.2.0a12, 2020.1.0b9 with package version: 4.3.0-preview.9, 4.3.0-preview.6

Working fine in:
2020.2.0a12, 2020.1.0b9, with package version: 4.3.0-preview.4, 4.2.3, 4.2.1

Environment:
Windows10 and macOS 10.14