It's a bit of a work around, for certain. The crux of the issue is the haxe error. So, what you need to do essentially is:
1) Export IPA from Stencyl (for App Store)
2) Delete the IPA from the location you exported it to
3) Go to your games-generated folder in your local stencylworks folder
4) Navigate to and open the Xcode file for the game you want to bundle the sticker packs to
5) In Xcode, delete the "haxe" target
6) Create sticker pack as you would normally
Hope that helps! Cheers.