Can you please replace the "." dot characters in the filename for "-" characters? I'm not sure why this filename is not expanded by Houdini at render time, but I'll investigate it. Perhaps the problem is related to the $HIP folder or the $HIPNAME file that have space characters or something like that.
Something like that as filename should work: $HIP/render/$HIPNAME-$OS-$F4, but you should try to don't use space characters in the folder or in the filenames.
Computer Graphics Software Develper
Octane plugin development and support: LightWave and Houdini