The climate component, by default, turns off when the simulation is running too fast for it to keep up. In the Climate tab you can change this behavior with the "Turn Off When Slow" toggle, and you can also manually set the timestep limit. If it's flickering back and forth, that's probably because the timestep is varying below and above the timestep limit.
Thanks for reporting the issue with the RCP scenario. These *should* still work, but it's certainly possible something is interfering.