since the introduction of Rhino 6, grasshopper is having issues with certain operations, which will cause GH to flag meshes as ‘invalid’.
Example (I know, don’t reduce a mesh like this, but it should not result in a ‘invalid mesh’, it’s just an example):
The only describtion we get is somewhat misleading: Mesh: ON_Mesh.m_F has degenerate double precision vertex locations.
Obviously it does have duplicate vertices (and not degenerate double precision vertex locations or I simply don’t understand the meaning of that) and the mesh really isn’t nice, I totally agree on that, but technically it’s still fine. But now Grasshopper (in Rhino 6) will completely refuse to do any further operation with this mesh.
While the nice and handsome Rhino 5 will just do its business as usual. Here works everything as expected. I have not tested this with the Mac Version.
This problem has been adressed here before but is still unsolved. I (and all of my students) would really love to see this issue to be resolved anytime soon. It is possibly one of the most demotivating bugs I have seen in a decade.