There is a bug in device and user mode where if one user’s id equals another user’s device, a call to the first user will ring on the second user’s device. I submitted a bug report but it was closed because “device and user mode is not supported”. This isn’t a configuration issue, it’s a bug in the code so beware - if you’re using device and user mode ensure your device numbers DO NOT OVERLAP with user numbers.
That is correct. D&U mode has not been supported by the core team in 5 plus years and has been discussed at length in tickets and forums. Their are lots of known issues with D&U mode.