Grain not working at higher DPI

Hi,

I have the grain effect on one of my shapes on illustrator. I recently changed the DPI of the file from 300 to 500dpi for printing purposes and the grain texture has disappeared? I've tried applying a new grain texture on the sahpe with the new dpi and when i go to edit intensity and contract, nothing is showing up to show a preview? Any help would be great! Also attached pictures of what the grain looked like and what it looks like now (very subtle difference- if anyone has advice on how make the grian more obvious that would be appreciated!).