This makes working in RStudio incredibly frustrating but (from y'all's POV), that sucks but it's not your problem. I thought. But I just realised that this issue isn't present in Libreoffice. Check side by side video of the same behaviour in both LO Writer & RStudio latest (1.3.935 installed today). With right arrow pressed, the cursor moves immediately and smoothly in LO, whereas in RStudio it lags before starting, and pauses intermittently for different periods of time.
I don't know enough (/anything) about how these two programs use the video driver differently, but IO figured this might be a useful diagnostic step in getting this resolved.
Thanks in advance!