I recently purchased a Nucleus+ and it was working fine. I wanted to expand the storage, however, and so purchased a Western Digital My Book Duo with 20TB. I have it in a RAID 1 configuration. When I connect it to the My Book Duo, however, it does not show up in either the Nucleus+ web admin page or under Storage in Settings. It does, however, turn on and off when the Nucleus+ turns on and off.
The solution was just a misunderstanding of where to find the USB storage. I assumed that (a) there would be some indication of its existence on the ROCK admin page like there is for Internal Music Storage – there isn’t, and (b) I assumed it would just show up in the Storage section of Settings, like Internal Storage does – it doesn’t. Instead you have to click “Add Folder” in Storage Settings, and there it is.