[DaveBlake]

I tried to change the advancedsettings.xml by adding:

<musiclibrary>
<itemseparator>;</itemseparator>
</musiclibrary>

But that had no effect at all. Multiple artists written in the <Artist> field as "Michael Jackson; Diana Ross" still lists as "[Artist] Michael Jackson/Diana Ross" in Kodi.
I quit kodi and rescanned the Library after changing the advancedsettings.xml, but it ran through in a flash and didn't seem to do anything. Do I really have to delete the whole library and rescan everything from scratch to make such a change effective?

The item separator is used in 2 ways:

a) Parsing various string tags e,g the artist name(s) from the ARTIST/TPE1 when music files are scanned into the library.
b) Building a single string for display from a union of artists or genres etc.

Use b) will take place immediately. Use a) only applies when the music file is scanned into the library. So if you have not changed the file tags then yes you will need to remove that source and re-add and scan it for item separator changes to result in "Michael Jackson; Diana Ross" been recognised as separate artists.

But also note that Isenguard does not trim names, so I fear "Michael Jackson; Diana Ross" with separator ";" will result in artists "Michael Jackson", " Diana Ross" (note the leading space).