Thanks for the extra information! One thing to note is that RStudio (synchronously) runs git status every time an RStudio window gains focus, to ensure that the Git pane is up-to-date. If the attempt to call out to git is slow for some reason, that could definitely be a culprit.
Do you see the same kind of slowness in projects not managed by git?
It might also be useful to use something like procmon to see if RStudio appears to be calling out to a particular child process when this sluggishness occurs (if possible in your environment).
The full event log might not be useful quite yet -- the waiting on get_events likely implies that the rsession process was stuck doing something (or waiting for something); hopefully we'll be able to figure out what that is.
(As an aside, if possible, you might try installing a daily build of RStudio from https://dailies.rstudio.com just to see if the experience is any better.)