After some testing and research I have concluded that this issue arises if the user clicks 'no' when asked the very FIRST time 'to allow the app to access the camera'. Apparently the app only asks that question once so any time after that the user isn't prompted with that question and the app automatically denies access to the camera. I have found that simply uninstalling and reinstalling the app OR upgrading the app will prompt you again to access the camera.
You can also toggle an apps' access to the camera on or off via the device's Settings. Go to Settings --> Privacy --> Camera, and look for Collector in the list.
As you discovered, apps only ask that question once. After that, you have to go to the Settings page to change your answer. Note also that an app will not be shown in that Settings list until AFTER you have answered that question.