You can ignore the octane messages. They come from the scene cleaning functions and are not dangerous at all. I've removed them for the next Octane 2020 plugin build.
About your issue with the rendered files, the problem is that you have at least one pass enabled (the Noise one) but you are not using the $OCTANE_PASS tag in the filename, so all the passes, including this one, are exported to the same file overwriting the beauty main pass.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini