It seems to me that the “nextNode.rendererData.m_RendererType == kRendererMesh” you’ve been seeing is not related to GI. We would however appreciate if you submitted a bug report with a repro case. It’s an error that should never happen™.
That said what are the “all the errors” that you mention? Any other errors in the console?
As for the profiler screenshot, it would be nice if you showed the details for one of the frames with a spike. At least it’s not the GI system itself that is the direct reason of the spike (it uses the red color in the CPU usage block of the profiler and there is no red). It could however be affecting the renderer by e.g. asking it to upload newly computed lightmaps.