Steps to reproduce:

1. Create a new template to using discovery to monitor snapshots on a ESXi host. Use vmware.vm.discovery to discover the host's VMs and use vmware.vm.snapshot.get to create an item prototype to get the snapshot data for each of those VMs. 
2. Use this template to discover snapshots on an ESXi 7.0.3 host that has at least 1 VM with multiple snapshots. 
3. Examine the data from the snapshot item and observe that the first snapshot size is actually the size of the VM, create time is correct.  The second snapshot size is actually the size of the first snapshot, again create time is correct for the second snapshot. Third snapshot is actually the size of the second snapshot,. The last snapshot size is not show by the item. 
4.  

Result:

From Zabbix snapshot Item:

**

First snapshot is ~20G

Second snapshot is ~865M

Third snapshot is ~540M

From ESXi:
First snapshot:

Second snapshot:

Third snapshot:

vmdk of the server showing that it is 20G:

:

Expected:
Expecting that the first snapshot size would be ~860M, 2nd snapshot ~535M, and the 3rd snapshot would be ~6.46G.