At some point I'm sure Home Music Share had a more traditional MiniDLNA view than USB Input but it sounds like that's changed.I didn't follow this discussion too closely but just wanted to note: Clicking on USB or Home Music Share and then the WiiM DLNA server opens exactly the same view on my WiiM Amp and on my WiiM Ultra.
There is no difference whatsoever.
It sounded like @cheznous was seeing different results on their Android and iOS device, which got me thinking. It could be that the Ultra/Amp is performing the traditional MiniDLNA indexing and the apps are translating that data to create the new view, just as it's doing now with Windows Media Sharing.
Maybe that's why the app needs to be on during scanning, not for the core scanning itself but to cache it in the app.
If this were the case then every device that runs the app would need to perform a rescan.