After updating to R 3.5.0 (Mac OS X 10.12.6) RStudio notebook behaviour has become flaky. Notebooks will sometimes fail to be generated at all, table formatting has been lost and there is frequently the message:
Error creating notebook: Exception caught: (SecurityError) : Blocked a frame with origin "http://127.0.0.1:44273" from accessing a cross origin frame.
This occurs even with a new .Rmd file and persists even with latest daily build (RStudio 1.2.612)
This is still a problem in RStudio daily build 1.2.650.
Downgrading to R 3.4.4 (completely uninstalling 3.5.0 and re-installing 3.4.4) did not help.
Downgrading to RStudio release version 1.1.453 fixed the problem.
But I don't recall this happening with daily build 1.2.618.
Somehow this has cropped up between RStudio 1.1 and 1.2.