Hello.

I have a laptop with 2 external screens connected via HDMI.
Then I took laptop, switched it off,  connected it to other 2 screens (DP and HDMI) and upon boot I had no panel at all.

> cat ~/.config/plasmashellrc
[Open-with settings]
CompletionMode=1
History=firef

[PlasmaTransientsConfig]
PreloadWeight=0

[PlasmaViews][Panel 29]
alignment=1
panelOpacity=0
panelVisibility=0

[PlasmaViews][Panel 29][Defaults]
maxLength=1920
minLength=1920
thickness=44

[PlasmaViews][Panel 29][Horizontal1050]
thickness=44

[PlasmaViews][Panel 29][Horizontal1366]
thickness=44

[PlasmaViews][Panel 29][Horizontal1920]
maxLength=1920
minLength=1920
thickness=44

[PlasmaViews][Panel 4][Defaults]
thickness=44

[PlasmaViews][Panel 4][Horizontal1366]
thickness=44

[ScreenConnectors]
0=DP-1-3
1=DP-1-1
2=HDMI-1
3=eDP-1

[Updates]
performed=/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/systemloadviewer_systemmonitor.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/maintain_existing_desktop_icon_sizes.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/klipper_clear_config.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/no_middle_click_paste_on_panels.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/digitalclock_rename_timezonedisplay_key.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/containmentactions_middlebutton.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/digitalclock_migrate_font_settings.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/keyboardlayout_migrateiconsetting.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/move_desktop_layout_config.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/unlock_widgets.js,/usr/share/plasma/shells/org.kde.plasma.desktop/contents/updates/keyboardlayout_remove_shortcut.js

Latest openSUSE Tumbleweed.

Kernel: 6.1.8-1-default
plasma-framework-5.102.0
plasma5-workspace-5.26.5
libQt5Core5-5.15.8

My workaround:
- kquitapp5 plasmashell
- Edit ~/.config/plasmashellrc and remove all entries under [ScreenConnectors]
- kstart5 plasmashell && kquitapp5 plasmashell

and panel appeared.

And in ~/.config/plasmashellrc I found:
[ScreenConnectors]
0=eDP-1
1=DP-1-1
2=DP-1-3

Another thing is, that selecting some screen as primary will make panel appear elsewhere.

I had to set 0=eDP-1 as primary to have it appear on 1=DP-1-1.