Hi All,
we've noticed this problem a couple of times through all Maya plugin versions since 7.4.
Create any type of Geo in Maya and apply an Octane material via Hypershade or viewport will assign the selected octane material but will not remove the default Lambert material.
And since you cant remove the default Lambert it will render the Lambert instead of the Octane Material.
OS: Windows 7 and 10 x64
Maya: 2015 SP6 and Maya 2016 SP5
Octane for Maya versions: All the way from 7.4 to 7.22