I am trying to perform a simple operation in Grasshopper, editing a series of simple meshes imported from Rhino through the Weaverbird plugin in Grasshopper, however what comes out of it is an invalid mesh. Anyone has any idea why this happens?
It seems there are duplicate mesh faces in your initial mesh input.
If you fix that in rhino from the first place, it should work fine.
And don’t forget to unify mesh normal directions.