I have found that several character combinations are not working fine if used to separate the $OCTANE_PASS and $OCTANE_LAYER from other tokens, like $F4. I'm investigating why this happens, but I am not sure why yet.
Usually, it is safe to use the "-" character, so if you set your filename as $HIP/render/tapes-$OCTANE_PASS-$F4 it should work fine.
Don't worry about the *** OCTANE API MSG: This source doesn't contain any primitives! warning message. Houdini 16 has introduced some changes in the OBJ nodes architecture and now the plugin is trying to extract some nodes that should not be rendered, like for example a bone node. Anyway, the scene should be rendered fine.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini