Black video feed sometimes?

We have an Ionic 4 app that works fine. We can do a video connection between the app and a web page and do a video call/connection fine. But sometimes the video steam from the app is just black. Nothing. about 10% of the time. The question is what might do this? What should I be looking for to improve it? We’re running Openvidu Pro 2.27.0.

Is it because the device (usually an iphone) might have an app open that was/still is using the camera still? Is that it?