Issues with panel & desktop in KDE

My setup:
Laptop + external display on the right. The external display is configured as main display.

The issue:
When creating a new panel, it works fine. Desktops behave like they should, widgets are present on the main display.
When rebooting, my panels move one display to the left, as if they where saved in 0-based array, and read from a 1-based array.
Panel moves from main to laptop display, and from laptop display to the ethernal hunting fields.

When all panels completely disappear, my main display keeps working as a desktop, but my laptop screen doesn't get a background,
refuses any folders or widgets i try to drag on them, and is not right-clickable. The function keys on my keyboard (volume up/down,
play/pause media, ...) are not responding witouth a panel present as well.

Locking the panel doesn't affect this behaviour, I seem to be up to date with packages, and I have no idea where to look for a solution.
I'm hoping that posting my problem here may help fix it, or at least give me some insight in the issue.
Please ask for any specs you deem relevant.

OS version: openSUSE LEAP 42.2
Kernel version: 4.4.79-18.26-default

[INDENT=2]Plasmashell version:
[INDENT=3]plasmashell 5.8.6[/INDENT]
[INDENT=2] kf5-config:
[INDENT=3]Qt: 5.6.1
KDE Frameworks: 5.26.0
kf5-config: 1.0[/INDENT]
[INDENT=2] Konsole version:
[INDENT=3]konsole 16.08.2[/INDENT]

Possibly, an upgrade to Leap 42.3 may alleviate this issue – the Plasma 5 environment is “newer” than the version delivered with Leap 42.2.

Yes, yes, the KDE delivered with Leap 42.2 is “stable” and “maintained” but, quite often repairs which address issues similar to one being described here do not get included in the patches made to “older” versions.