Didn’t see any obvious code so solved it by watching to see which blocks are stressed when the draggable is lowered.
First I thought it would a sort of lotery : 1 chance over 256. A waste of time ! But ... Spoiler: Spoiler 1 I looked better at the starting view and saw how the draggable was blocked Spoiler: Spoiler 2 After that, I figured out I had to fill every other "window"