I have seen my clowns mouth the nems before.
My largest nem now is the one the clowns leave alone the most?
The other two are 1/2 the size BUT they were one a year ago(much bigger) and split!
Even then the clowns preferred the nem!
They have always preferred the rose over the yellow for me?
if it is not the clowns pestering the nem then my next thing to look at would be lighting?
How long have you had the nem?