This is likely due to how Swinsian writes to the m3u8 files, in which case this is something we would need to look into further. I've added this to our roadmap.

https://support.mixo.dj/t/import-swinsian-m3u8-files

However, we can import iTunes playlists, so if you are able to import these files into iTunes you may be able to export them with the correct format that MIXO is expecting.

Let me know if this works.