I have six different cameras (from flood light cameras to wired and wireless (solar cameras). These symptoms are experienced in all of them.
Sometimes when I launch the live view in the app, the video is not displayed (it shows the loading icon), but it does record the video and I can see it later in the timeline. Killing the app and restarting it fixes the problem sometimes, but not always.
Additionally, some motion detected videos are recorded just completely black. The app version is 5.50.1. All cameras show that their firmware is up to date.