In the meantime it’s fixed.
There is in windows a second place for Indexing options. Search for Indexing options in the start menu, and make sure the location of your music is added to the list:
So even when a folder is marked as ‘Allow index’ in the advanced attributes stated by @Slak_Jaw , if that location isn’t a child of any of the locations of Indexing options, then it won’t be indexed.
