Comment # 5 on bug 964725 from Jaroslav Mar�k

It is not problem of monitors order. That is correct.
Explicit definition of /etc/X11/x�rg.conf.d/50-monitor.conf - in my case:

Section "Monitor"
        Identifier      "VGA1"
        Option          "LeftOf" "eDP1"
        Modeline "1680x1050_60.00"  146.25  1680 1784 1960 2240  1050 1053 1059
1089 -hsync +vsync
EndSection

Section "Monitor"
        Identifier "eDP1"
        Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088
1120 -hsync +vsync
EndSection

Section "Monitor"
        Identifier "HDMI1"
        Option "RightOf" "eDP1"
        Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088
1120 -hsync +vsync
EndSection

Section "Screen"
        Identifier "Default screen section"
        SubSection "Display"
                Virtual 5520 1080
        EndSubSection
EndSection

does not solve this problem. It solves only broken login Plasma dialog.
Situation is the same - my monitors layout:

left - Desktop layout, wallpaper 1
center - Folder-View layout, wallpaper 2
right - Desktop layout, wallpaper 3

and after reboot is still broken:

left - Desktop layout, wallpaper 3
center - Desktop layout, default theme wallpaper
right - Desktop layout, default theme wallpaper.

Before 50-monitor.conf I have checked current status with xrandr -q and it was
correct:

VGA1 connected 1680x1050+0+0
eDP1 connected primary 1920x1080+1680+0
HDMI1 connected 1920x1080+3600+0

Problem is lost layout-context in case of every monitor settings (on desktop:
right mouse button -> Desktop settings -> Layout)
Monitor ordering is always correct, resolution is never broken.

J.M.