SUMMARY
If the positions of monitors are swapped around in System Settings, the "Window to Previous Screen" and "Window to Next Screen" shortcuts adhere to the old positions of monitors instead of the new positions. However, if this is done manually using xrandr, the shortcuts work as intended. Therefore, I think that System Settings is misbehaving.

STEPS TO REPRODUCE
1. Under "Shortcuts > Shortcuts > KWin", add a shortcut for "Window to Next Screen".
2. Under "Display and Monitor > Display Configuration", place three monitors next to each other. Let's call them A, B, C, from left to right. Apply settings.
3. Open any window on monitor B, and use the "Window to Next Screen" shortcut. Verify that the window moves to monitor C, as expected. (If not, it may help to restart the computer, so that the order A, B, C is loaded from the start.)
4. Under "Display and Monitor > Display Configuration", swap the positions of monitors A and C, so that the order is C, B, A.
5. Open any window on monitor B, and use the "Window to Next Screen" shortcut.

OBSERVED RESULT
The window on monitor B moves to monitor C. (To the left!)

EXPECTED RESULT
The window on monitor B moves to monitor A. (To the right!)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 5.23.5
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
If I change the order of monitors using xrandr, this bug does not occur. Concretely, the following steps give the expected result noted above:

1. Under "Shortcuts > Shortcuts > KWin", add a shortcut for "Window to Next Screen".
2. Run
   ```bash
   xrandr --output DP-0 --mode 2560x1440
   xrandr --output DP-5 --mode 1600x900 --left-of DP-0
   xrandr --output DVI-D-0 --mode 1280x1024 --right-of DP-0
   ```
3. Open any window on monitor B, and use the "Window to Next Screen" shortcut. Verify that the window moves to monitor C, as expected. (No computer restart should be necessary.)
4. Run
   ```bash
   xrandr --output DP-0 --mode 2560x1440
   xrandr --output DP-5 --mode 1600x900 --right-of DP-0
   xrandr --output DVI-D-0 --mode 1280x1024 --left-of DP-0
   ```
   (Note that "left" and "right" have been swapped relative to step 2.)
5. Open any window on monitor B, and use the "Window to Next Screen" shortcut.