@_jis_ looks like the Synology cloudstation app responsible for syncing to the NAS might be the culprit here - within /Music/ there's a hidden .SynologyWorkingDirectory folder which is: 77915 items, totalling 11.4 MiB (11,980,733 bytes)
Absolutely absurd. The only folder within that is #SynoRecycle. Deleted that, which looks like it's the same few folders copied infinity times, potentially 50% of the folders are a copy of some small notification sounds I synced and removed one, a week ago. Terrible coding from Synology and seemingly I'm not the only one. Good thinking jis for asking about this.
Used space 318 GB
Available space 49 GB
Totally 6599 directories and 58894 files.
File system checking finished. No errors found.
A .nomedia file was somehow created automatically in /Android/data/; should this instead be in /Android/data/com.synology.dscloud/ ?
Should I delete it and see what happens?
Thanks again for your input!