SUMMARY

In system settings > display configuration, when I drag my second display on top of the first to mirror it, it will snap to a position that it initially reports as 0,0 while snapping it into place. But clicking on the screens again will show that one of them (usually the primary display) is actually at 1,0 instead of the expected 0,0, and there is no way to make it properly snap to 0,0 within the settings GUI as it will always snap back to that 1,0 position no matter which monitor you drag onto which or from where. Checking the newest profile in ~/.local/share/kscreen confirms that the position is at 1,0:

        "pos": {
            "x": 1,
            "y": 0
        },

Both displays are 1920x1080, connected to the GPU directly and in the same orientation, both at 100% scale with no overscan. One is connected by Displayport and one HDMI, and I've confirmed the same behaviour with another DVI-connected monitor as well. I don't have a second Displayport monitor to test dual Displayport or additional HDMI ports on the GPU to test dual HDMI. The Displayport monitor is a 165hz freesync monitor and the others are 60hz, but I've tried disabling freesync and setting the monitor to 60hz and it resulted in the same behaviour.

This causes various issues. Occasionally randomly, but usually after launching something fullscreen, all icons/widgets on the desktop will disappear and the wallpaper will be shifted over one pixel. After this has happened, clicking on the leftmost and rightmost pixel columns of the screen will shift the wallpaper back and forth one pixel and alternatively reveal or hide the desktop icons, as if revealing the second display underneath and slightly offset from the first. Once this behaviour has started, clicking the leftmost/rightmost pixel columns on the screen will always do this until a restart, at which point mirroring will seem to work again for a while.

This issue seems to occur on both Wayland and X11, but on X11 is easily fixable by the "Replica of:" setting in Display Configuration which perfectly mirrors the displays every time. On Wayland just due to the way displays are handled differently there is no such setting, and manually editing the value in the profile in ~/.local/share/kscreen and then running "kquitapp5 plasmashell || killall plasmashell && kstart5 plasmashell" doesn't solve it either. In fact, if the desktop is not already misbehaving and you do this, it will cause the bug to occur immediately, I find.

STEPS TO REPRODUCE

1. Drag and drop a display of the same resolution and orientation on top of another in the Display Configuration GUI in Systems Settings
2. The display you are moving will snap to the same position as the first, and while still holding the left mouse button down, the position of the display will be reported as 0,0
3. Let go of the left mouse button and then click apply
4. Then keep double clicking on the display to reveal its position and the position of the display underneath it, one of them will show a position of 1,0.
5. Go to ~/.local/share/kscreen and check the newest profile saved there then look for "pos" and check the reported x/y values for both displays. One of them will be 1 instead of 0.
6. Try to edit all "pos" values for both screens to be 0, save, and then run: 
kquitapp5 plasmashell || killall plasmashell && kstart5 plasmashell
If the bug isn't already occurring, it will occur now.

OBSERVED RESULT

One of the mirrored screens, usually the primary display, is at position 1,0 instead of 0,0, sometimes causing misbehaviour of desktop icons and wallpapers, making the wallpaper shift by a pixel column and desktop icons disappear. Manually editing the position in the profile will not solve the issue.

EXPECTED RESULT

Both monitors are at position 0,0 and are perfectly mirrored.

SOFTWARE/OS VERSIONS

Fedora 36 KDE Spin, Kernel 5.17.11
KDE Plasma 5.24.5
Kscreen 5.24.5
Qt Version 5.15.3