KB3169: Changed block tracking cannot be ... - Veeam Software
https://www.veeam.com/kb316906.05.2020 · After upgrade to Veeam Backup & Replication 10, the Backup of a VM using Cisco HyperFlex Snapshots completes with the warning "Changed block tracking cannot be enabled: one or more snapshots are present" if a Sentinel snapshot is already present. The described issue with Cisco HyperFlex Snapshots was resolved in Veeam Backup & Replication v11.
KB1681: VM Loses Connection During Snapshot Removal
https://www.veeam.com/kb168104.10.2012 · Veeam does not remove the snapshot itself, Veeam sends an API call to VMware to have the action performed. The snapshot removal process significantly lowers the total IOPS that can be delivered by the VM because of additional locks on the VMFS storage due to the increase in metadata updates, as well as the added IOP load of the snapshot removal process itself.