problem (horripilating ! ;-)):
on logging, icons position on desktop changed since last logoff.
Mainly some (but not all) icons moved from their position somewhere in the screen to the first top line, aligned in sequence.
plasma desktop appearance is on "display directory"

Of course, no manual icons moves where done before logon/logoff and icons where "locked" and desktop graphic components also

analysis :

- modification of "~/.config/plasma-org.kde.plasma.desktop-appletsrc" in the [Containments][1][General] section has occured
- further analysis in the KDE 5.36.0 sources locates usage of this file by :
	/KDE5/src/kactivities-5.36.0/src/imports/activitymodel.cpp
class BackgroundCache {
    public:
        BackgroundCache             ()
            : initialized(false), plasmaConfig("plasma-org.kde.plasma.desktop-appletsrc")
        {
        
I suspect a copy/paste typo in emitActivityUpdated () the preceding function in the cpp listing ;
but maybe its correct because I haven't done in-deep code review.

    template <typename _Model, typename _Container>
    static inline
    void emitActivityUpdated(_Model *model,
                             const _Container &container,
                             const QString &activity, int role)
    {
        auto position = Private::activityPosition(container, activity);

        if (position) {
            emit model->dataChanged(
                model->index(position->first),model->index(position->first),
                role == Qt::DecorationRole ? QVector<int> {role, ActivityModel::ActivityIcon} : QVector<int> {role}
            );
        }
    }
maybe should be modified as follows :
            emit model->dataChanged(
                model->index(position->first),model->index(position->last),

I don't want to recompile KDE to check if this can solve the problem because I don't have a development platform.
But please let me know if this is the answer ...