I use Manjaro-i3, and I had the same problem with Manjaro-KDE, and I have this problem everywhere (when I use chromium, terminal, or any other software).
When I use the mouse (external wireless mouse) the scroll goes up and down quickly and doesn't scroll in the right direction, and I have to click the scroll bar by clicking and drag it down or up to be able to scroll using the mouse. However, when I use the Touchpad, it's perfectly fine to scroll down and up smoothly.
I thought it might be a hardware error, but when I used the same mouse on Fedora it was fine and scrolled smoothly exactly like the touchpad.
Any Ideas how to solve this problem?