Issues apply to the following: 2019.15 & 2020.1 RC2.
Geometric Primitives in Stand Alone do not currently work when exported as ORBX in latest Octane Blender builds for Blender 2.8 / 2.82.
Another even more pressing issue is ORBX proxies will fail if a PLACEMENT node is used. This of course prevents us from exporting as a proxy any transforms or animations done in Stand Alone. It also limits the complexity of the scenes that can be exported - pretty much limiting it to single objects.
Neither of these limitations ever existed in Octane Blender for Blender 2.79 (I have tested and experienced no issue with 2019.1.4 / 8.6).