I solved it!! found this old post here, and then tried this path, and it worked!!
this.http.get('file:///android_asset/www/assets/JSON/ingredients_exhibition.json')
this also worked for my images!
imageUrl: 'file:///android_asset/www/assets/img/0.jpg'
(I still have no idea why part of my images work with this path: “…/assets/img/level4.png” and some with the other path… but 