I have updated my original explanation on Github: https://github.com/mendix/ux-theming/blob/master/README.md#mendix-8-caveats
Long story short: You should point to the 'web' folder in styles, not styles itself. The problem is with the 'native' folder. I have been debugging this today and this solution should be the fix.
Sorry, works for me:
I managed to reproduce your bug, and I offer a solution:
The Gulp.zip file needs to be unpacked into the ROOT of the app, not into the THEME folder.
Then everything runs flawlessly.
EDIT: I use “yarn” and not npm, it’s the same thing, your command would be ‘npm run dev’
I didnt even know there were different ways of people compiling their sass :D awesome to see different solutions.
Im going to do some more testing, thanks for the insights.