The problem can be that at some point the object mesh topology changes between two frames, and the plugin can't update the mesh deformations or compute the motion blur. Can you please try to render the scene configuring the ROP node in "Full Scene Reload" mode? This problem should be reported in the Octane log, if you enable it in the plugin options panel.
In any case, if you can't resolve this issue and if you can send me the scene, I could take a look at it to check what could be the problem.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini