@jonas Good call -- I've traced it to the Linux applet Enhanced Sound, as removing that from the panel resolves it instantly! Thanks, I'll get onto claudiux about it, as I thought I'd turned off any features that involve music players...

@mncroc
Do you know when / how the duplicates occurred?

If you used the organize feature prior to 1.0.23, it might be caused by a bug that is fixed in 1.0.23, but the duplicated are not removed automatically.
To manually remove duplicates, see.:
https://wiki.strawberrymusicplayer.org/wiki/Find_and_delete_duplicates_from_the_collection_database
I suggest to make a backup of the database file (~/.local/share/strawberry/strawberry/strawberry.db) before attempting to modify it.