locked icons move hwn starting KDE

I have over 30 icons in my plasma desktop.
Since I have upgraded from 42.3 to 15 ob login they move to the top of the desktop.
Not all of them, some of them (it seems they are always the same ones) remains at their position.
I have set the lock-widgets and icons-locked and if I try to move a icon I can’t, it return to it’s position, but anyway, when reboot and log in again, the icons are moved (except some times the aren’t).
Any clue why may be happening?