Kbuntu vertical display change, icon layer

The vertical display on my Kbuntu 22.04 has suddenly changed.

The size of the deskop wallpaper is fixed and normal, however the layer containing desktop icons has expanded vertically, with a scroll bar on the right side, which will move the icons up and down.

Presumable, there is a setting somewhere that can be reset so that the icon layer is the same size as the wallpaper. Where is it??

Further testing:

The vertical size of the icon layer appears to be determined by icon placement at the top and bottom. If there is a row of icons at the top, the layer appears to "need" at least one icon below the bottom of the screen for a bottom row of icons to display on the screen. Dragging the below screen icon to mid screen seems to be not allowed, as it jumps back below the screen. A weird behaviour.

If I arrange the icons in a certain pattern, apply 'Lock Icons' and reboot, the icons are scattered. This suggests the "layer" containing the icons is corrupted, what to do to fix it??

I have learned that my reference to icon layer is more accurately the desktop Folder view/mode which is misbehaving . . . .

Further testing:
The problem seems to be caused by something re-writing/corupting two files:

.config/plasmashellrc and .config/plasma-org.kde.plasma.desktop-appletsrc

If I arrange the icons and then change the properties of these two files to view only and re-boot, I get a black screen with a message to saying:

Configuration file .congig/plasmashellrc not writable

When I press OK the desktop wallpaper appears, which is followed by the folder view with the icons miss-arranged, and then the icons reset to the correct positions.

What is corrupting these files??