I read somewhere that the new Apple File System (APFS) is causing this. Introduced with High Sierra. If you have an old songlist it's ok but when it's rebuild it's a mess. If you open de songlist (it is saved with the songfiles) it shows you the 'haphazardical order you mentioned.

At the same time my 'recently loaded song' developed Alzheimer. After a few hours it's empty again. Seems related.

I was hoping this would be resolved in the 2018 update. But do I understand correctly that it hasn't?