Removing vertex selection for BMesh

As with normal mesh manipulation via the Blender Python API, when using the BMesh object to deselect vertices, it is not enough to simply change the value of their "select" property to the opposite. To deselect the vertices of the BMesh object, the "select" value must also be changed for the edges and polygons adjacent to them.

Read more: https://b3d.interplanety.org/en/removing-vertex-selection-for-bmesh/