\n should work always works for me an example of how i use it
titletext ["blah blah\n blah blah blah", "plain down", 1]
maybe it only works on certain types of text as i usually use titletext in your example you are using titlecut maybe changing it to titletext may work
also i dont have a space between the last word and the \n so try that too
also are you using plain down ? or something else maybe that effects the command
not sure about any of those suggestions but worth trying maybe ?