I'll try to keep this simple:
I have (amongst others) a 3TB volume on my Dell Equallogic SAN.
It is thin provisioned, with 2.34TB in actual use.
I have it set to keep 1 snapshot but at present, number of snapshots = 0
Despite there being 0 snapshots, the snapshot space is reporting as 3.27TB in use (see attached screenshot)
It is backed up by VEEAM (may or may not be related) but no backups are currently running.
This is a mystery to me.