I have the same problem (IOS 11.1.2 iPhone 6) with Shopping list. Two items added by voice to list with two existing items. Alexa correctly read back all 4 items but the iPhone app still showed only the existing two. After I power-cycled the phone, all 4 items were listed in the app. I deleted the last two and Alexa correctly told me that only the original two were now in the list. The app appeared to be "stuck" displaying the shopping list and allowed limited navigation, always returning to the initial 2-item shopping list until the power cycle.