Hi, I'm experiencing a similar error to this user's post from October of last year:
I'm running RStudio version 1.1.456 on a Macbook Pro running macOS 10.13.2. I'm just clicking / editing a .R file after loading a few packages, and then RStudio hangs and Activity Monitor says it's using 100% of the CPU. Somehow RStudio's internal code gets caught in an infinite loop I guess?
The .R file is a Dropbox file, but it should be downloaded locally to my machine, as it has a green checkmark next to it.
I'm able to highlight and run several lines within the script, but then afterward I'll click, delete, highlight, or type text in some fashion that unpredictably leads to the rainbow circle and Activity Monitor reading 100% CPU. It then varies whether it resolves itself within 30 seconds or pauses for much longer.