RStudio for Mac
Version 1.2.1335
Build 1351 (f1ac3452)
In the editor area, it happens when there are some long-lines. It seems that the horizontal scrollbar is over the vertical scrollbar and the text of the last line.
When the cursor goes to the last line, it just goes under the horizontal scrollbar. Then we can't see the text of the last line. See the attached picture.