I have two monitors, DP-3 with 2560x1440 resolution, and HDMI-1 with 1920x1200 resolution. I want HDMI-1 to be displayed to the left of DP-3. When I run xrandr --output HDMI-1 --auto --right-of DP-3 everything displays as intended, but when I use --left-of the entirety of what originally displayed on HDMI-1 gets displayed on the DP-3 monitor and the rest of what was originally displayed on DP-3 extends into the monitor of HDMI-1.
There is another thread here from a few years ago where someone was having a similar issue, but the solution posted doesn't work for me. It also is never explained why --left-of apparently messes with scaling.
I don't know if this helps, but I'm using i3 and LightDM as my windowing and display managers