Library location in iTunes for Windows won't "stick", and related concerns

I have iTunes from the Windows Store running on my Windows 10 PC. I subscribe to Apple Music and iCloud Library/iTunes Match. My iTunes Music Library has long been located at D:\Music, with the actual media in D:\Music\iTunes Media.

Now all of the sudden iTunes show almost all my music with exclamation marks beside them, and Edit-Preferences-Advanced the iTunes Media Folder location is shown as D:\Music, the folder above the current media folder. I have tried to change the folder location to D:\Music\iTunes Media; it seems to accept this, but if I open the dialog again, the folder is again set to D:\Music.

I proved that iTunes is seeing this as the media folder because folders I dropped into Automatically Add to iTunes puts new music in D:\Music, and these files don't have exclamation points.

I addition, I was seeing some songs that had two entries in iTunes, as if they were duplicated, but pointing to the same file in the same folder. That is, duplicate files are not present in the media folders. These folders were in the "new" media folders under D:\Music, not the older iTunes Media folder.

I can certainly move all my music files to D:\Music, but I don't understand the double entries, why the media folder entry changed, or why iTunes won't accept my correct media folder. Consolidating the library does nothing; when D:\Music is selected as the media folder, the music in D:\Music\iTunes Media doesn't move there when I tell it to consolidate.

There has been no loss of music or playlists, but I'm afraid my iTunes database is going bad. My previous iTunes libraries are over a year old, so I'd rather not have to use them, as I've added a lot of music since then. I have a backup of the D:\Music folder done just today, so the current setup is safe.

What should I do to bring everything back to stability? Should I wipe everything, create a new library, and bring it all back from the iCloud Library? Just move the files to D:\Music? Use the version of iTunes found on the Apple Website instead of the Microsoft store version? I am unsure of which way to go now.