Animate no longer exports images as a spritesheet

Hi,

I created some HTML5 Ads a couple of months ago with all images exporting into a single sprite sheet without any issues. I have tried to use the same Animate file but with the images replaced for a new batch of Ads however the images will not export as a Sprite sheet and will only export as seperate JPG's. I have also tried re-exporting the old ads and they also no longer export as a sprite sheet either.

The publish settings are set to export as a spritesheet but it seems to no longer work. Can anyone help resolve this issue?