We are aware of some issues uploading large music libraries.

I've subscribed you to the idea for updates as and when they're ready:

https://support.mixo.dj/t/importing-large-libraries

I can see on our end that you have synced 15,000 tracks, does your cloud storage reflect this?

Make sure to update to 0.9.0 which is the latest version of the app and then try again. I would advise however, to upload in smaller chunks for now, but we are working on this issue.