So Camera control's have a property called Camera, which is used to tell the app which camera (since many devices have multiple) to use. This defaults to 0, and is usually the rear camera on the phone.
Try having this property be dynamic for each control. Something like
If(
App.ActiveScreen = Screen1,
0,
-1
)
This may trick the other controls into unlocking the device's camera. It may also continuously prompt to allow use of camera - not sure.
Could you consolidate the Camera functionality into a single screen and route to that screen from the others? If not, I recommend trying the AddPicture control over the Camera control. It has a number of advantages, and behaves well on mobile devices. This may remedy this particular issue, as well.