Hi, current Octane materials are not compatible with 2.23.2 - 2.8. You can see the technical details in their release post:
THIS MAJOR VERSION'S SCENE FORMAT IS NOT COMPATIBLE WITH PRE-2.0 PLUGIN VERSIONS! DON'T SWITCH THE CURRENT CRITICAL PROJECTS TO THIS AND LATER RELEASES!!!
Read the changelog of this 2.X branch and discussions in previous threads of 2.X versions.
You can use the materials export/import to/from LocalDB to transfer the materials between 1.X branch versions and current versions.
We'll adapt our libraries once they release the stable version.
If you convert your scenes, please note there is a known bug in Octane, which takes Forest materials not from Geometry->Material
as it should be, but directly from the Custom Object. So be sure your custom objects has the right material assigned (they can be select using right menu->Select Forest Custom Object