Whenever I'm using two side-by-side windows, part of the leftmost
character in the right-side window is hidden. 

This is when I use the Gnome HiDPI window scaling set to 2 to make text
readable on my 4K screen.

The problem is visible with emacs -Q --no-x-resources.
Turing on display-line-numbers-mode hides the problem, at least with the
default settings.

To reproduce:
emacs -Q --no-x-resources
M-x split-window-right
toggle the hidpi window scaling between 1 and 2.

I'm trying to attach a screenshot.

/Ola