Starting with Veeam Backup & Replication 11a, the task scheduler now uses the dedicated threshold of a maximum number of open VM snapshots per vSAN datastores, with the default limit of 32 snapshots. You can control this setting with the VSANMaxSnapshotsNum (DWORD) registry value under the 'HKLM\SOFTWARE\Veeam\Veeam Backup and Replication' key on the backup server.
Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication
Value Name: VSANMaxSnapshotsNum
Value Type: DWORD (32-Bit) Value
Value Default Data: 32