I have no idea why or any better solution until now, but if you are experiencing that your materials are only white in the octane liveviewer you can try to change the projection-style of your material from (standard) uvw-mapping to spherical mapping (or any other type) in the c4d attribute window.

Looks like this is a problem with step-files when you change some settings in the import-dialog. i reseted the settings to standard and the problem is gone. I unfortunately can´t reproduce the settings.