you might find alternative solutions with code, maybe involving some Stop/Pause timer between items [edit] GHPython-counter from 0 to a value - #3 by AndersDeleuran [/edit]
but trying to redo your file, it does not happen on my PC that any item is repeated twice, not at the Data output of the Loop, not at the List Item directly:
ABCD_Loop.gh (12 KB)
I am not able to reproduce the problem you are encountering