To be honest, it’s very difficult to understand Apple rejections. They are notorious for being difficult and rejecting apps for even the most minor of things. So, it could be the usage of in app browser. Or my suggestions about the UI.
I suggested the UI changes because we’ve definitely heard of other rejections in the past from Ionic community members. I do plan to write about this topic soon though, to raise awareness.
Keep us posted here, if possible on the status! thanks.