Hey!
I think this may be a bug that I've fixed but haven't published the patch for. I fixed it just before I went on a trip so I wasn't able to push it just yet...
I'm assuming this is the Ultra shader being used with Unity UI... if that's the case, please go into the file for the Ultra shader and delete the shadow pass entirely. It's the final pass on the shader, and the extra "ZWrite" call should be deleted, too. Sorry I'm not just sending the updated script, but I can't until I'm back next week.
Otherwise, try tweaking the parameters on the sketchify script? I'll be able to give this a closer look soon!