Thanks for the suggestion. I tried all of that in all kinds of combinations, but it doesn't change the outcome.
Quite literally it seems like Cinema 4D doesn't load the 3.08.3 plugin properly. I quickly tried it with 3.08.2-R3 and it worked like a charm. So, given that everybody else's 3.08.3 plugin seems to work fine (and that they are not on R18), there should be something wrong with the "c4dOctane-R18.cdl64" file for version 3.08.3.
The biggest giveaway is - as I said - that the Octane menu entry in Cinema 4D's top bar is empty. Have a look at the screenshot below:
So even though Cinema recognises some of the Octane plugin, it doesn't load it properly, otherwise all the options would be there.
Aoktar, could you please look into this? That'd be much appreciated.
Custom PC, Intel Core i7-6800K, 32GB RAM, 3x MSI GeForce GTX 1070 Seahawk EK, Windows 10
HP Omen 17, Intel Core i7-7700HQ, 32GB RAM, 1x NVIDIA GeForce GTX 1070, 1x EVGA GeForce GTX 1080 Ti Hybrid (eGPU), Windows 10