I'm afraid that this seems a crash at render time, from the Octane core, although it is really weird that no CUDA or other errors are reported in the log. Octane 2018.1 and 2019.1 have a lot of fixes on the denoiser side, but I'm not sure if you have access to these Octane versions.
If you can send the whole scene, I can take a look at it here to try to reproduce the problem, but could be great to know if this problem has been already fixed in the latest Octane versions.
Thanks,
-Juanjo