Starting with Veeam Backup & Replication v9.5 U3 (18.104.22.1686), a setting was added to allow for the configuration of a delay between the detachment of hotadded disks and the request for snapshot removal. This delay can be configured using the following registry value:
Create On: Veeam Backup Server
Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: HotaddTimeoutAfterDetachSec
Value Type: DWORD (32-bit) Value
Value Data: 60
The delay is measured in seconds and may need additional adjustment based on the environment. In most cases, 60 seconds has been plenty of time for disks to detach from the proxy before the snapshot removal request was issued. A smaller delay may also work. However, a larger delay may be required in some environments.