I have seen a comparable issue from time to time. In most cases it works fine, but in some cases the added camera disappears. When I add a camera it all works fine. The camera is recording etc. After a couple of days, when NCS is restarted, the camera is gone, and there is no trace anymore.
Really strange, and I can't pinpoint the issue.
It looks like, but I could be wrong, that NCS does not save the config file when adding a camera, but only when you shutdown NCS. So if NCS is running for weeks (with the new camera), and then crashes, the change is gone.
I would suggest that the file is written right away, and pop up an error if there is any issue writing the change. Also a consistency check on startup of the file would be a good idea.