Hi
I installed on the same machine Cinema 4d R19 and R21
In R19 Octane works properly
I installed the plugin also in R21 but (after sign out in R19) when I sign in, I see in left bottom corner of Cinema "Plugin activation OK" and after that Cinema close itself
I installed other plugin like X-particles and Cycles4d and they work well
I used the 4.05-R7 version plugin