It's probably not the issue here, but some time ago with the old exporter I saw a situation similar to this. In my case, it turned out to be an issue of Octane misinterpreting the normals. When I told the exporter to send the normals, the frames with missing textures were fixed.
I know it does not apply directly, but I figured I'd throw it out there in case it may indirectly be of some help.