The issue will be resolved with the release of DDBoost SDK 2.6.5.1 by EMC. The necessary compatible DDOS version for the fix is DDOS 5.4.6.0, and it would also need to be released.
The new version of the plugin will be used in Veeam B&R version 9. On earlier versions of Veeam B&R, DDOS, and DDBoost Plugin, connect to DataDomain device over CIFS protocol to work around the issue.