Even with the latest stable release (3.8-12) I’m pretty sure the share size being reported isn’t accurate when snapshots are involved, for instance I have a share that reports 280GB where as it’s actually over 1TB in size.
Equally I just deleted some of the older snapshots and the webUI claimed over 800GB of data would be deleted which is extremely unlikely.
The dashboard also shows about 380GB of data in shares where as in reality it’s probably closer to 2TB