Yeah, I wouldn’t have noticed as I usually stay well within the +- 5% range and usually keep it to +- 2-3%.
Unfortunately I can’t check to see if I have the same problems. Hope one of our other readers can check his/her setup and tell you what they come up with.
There is a tool in Windows (not sure for Mac but presumably there is something there as well) called Performance Monitor (perfmon.exe) that lets you record things like CPU and Memory load over a period of time.
You could run that in the background and then create the unwanted behavior in RB. You can now look at the data in Performance Monitor to see if the moments RB gets into trouble coincides with max CPU and/or Memory load.