After a little more testing it's clear this actually isn't an RStudio thing and is instead a problem with GNOME Text Editor. It's still very weird.
- In Rstudio Desktop, open a new R Notebook and begin work. Leave active cursor in the notebook tab.
- In GNOME 3.24.2, switch to a large open file in Text Editor with Alt+Tab.
- Copy text to clipboard.
- Switch back to RStudio.
Rstudio Desktop is responsive, blinking cursor in R Notebook tab.
Rstudio Desktop unresponsive, GNOME prompts to "Wait" or "Force Quit." Sometimes Rstudio recovers, sometimes it does not and the process must be killed.
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/538.1 (KHTML, like Gecko) RStudio Safari/538.1 Qt/5.4.0
On Fedora 26