You need to activate tesselation in the octane parameters tab of the object (by adding an octane param tab at object level so). I guess it is related to a way of interpreting geometry.
Yes, Octane doesn't support complex ngons or polygons with holes, so the plugin has a function to tessellate these polygons to make them compatible with Octane. It is not enabled by default because this operation can be slow, and usually it is not needed at all for quads or simple convex polygons.