Could you open a new thread for RT/IV issue and post a simple scene, video, describing steps to reproduce, full specs... showing, exposing the bug.
IIRC, there was such a bug some time ago, but for now (v10.1) runs well...
Although during more intensive, complex workflow, C4D can and occasionally IR/IV does stall (can't keep up and doesn't refresh) as it seems it's still highly sensitive to hierarchical order when generative processing and procedural/ key-framed animations are involved. But then, on 2nd action IR/IV responds again. (?)