I had this bug too. when I installed and uninstalled another camera app from play store, then the main ASUS camera app started showing the message ''camera cannot flip'' when I use the selfie camera. ASUS has to fix this bug...
It could be that your camera is not working 100% and that the resistance when flipping up is to high, making the software believe that there's something blocking it. For this issue, it is best if you contact ASUS support . It's very important that you tell them how often this happens. Like, it will get stuck in one flip out of ten when you continuously test with different software https://www.asus.com/support/CallUs/ https://www.asus.com/support/Product/ContactUs/Services/questionform/?lang=en