As we know your CBT mechanism now don't work when any of Windows Failover Cluster node have troubles, have extended maintance period or working with PRO mechanism to save power. See this thread: https://forums.veeam.com/microsoft-hyper-v-f25/cluster-change-block-tracking-t26725.html
Now when we have one node down we experiense extreamly high load of Storage because on every backup Veeam reads all data of VHDs. From this point we cannot mantain cluster in backup time at all because of performance issues.
I assume that this mechanism needs some changes - it must work even nodes not accessible.
The best solution from my point is storing CBT data on cluster resources so this data can be accessible any time when cluster works fine.
Another solution - ability to recreate CBT data when node offline for a long time. So only first backup will reread all data and next backups will use CBT again.
Hope you put in on board.
Nail Mukhametshin | System Engineer | R&D Services Infrastructure Development | Kaspersky Lab