That “refreshing” behaviour is not expected. From your video it seems like the whole camera manager is failing (since all the stream options are disappearing, not just the ones for your USB camera).
Can you check the video manager logs in the Terminal page (ctrl+b, s, then press up to get to video manager)? It would be helpful if you could share a screen recording of those logs with the Video Streams page open in a separate window, and manually reload the Video Streams webpage.
It would also be helpful if you could provide and/or check your system log files, in case the camera is repeatedly losing connection or something.