Snapshot size being reported as Zero bytes: Should I be concerned??

We usually monitor job and work on failures; however; I was investing a partial sucess warning on a server and happened to notice this zero byte snapshot for all the servers for this customer; I understand for a powered off VM this could be true however it appears to be a bit weird that the backup size has changed from one backup to another however the snapshot size is still zero. shall I be concerned and investigate it further? 

It seem to be happening to any VM which is hosted on VSAN storage for this customer normal datastore appear to be showing the correct snapshot size