I doubt this has anything to do with VSS.
First steps: if running SSR 2011, make sure the machines are running latest service pack - SP3 (version info will show 10.0.3). If running SSR 2013, make sure the machines are running latest service pack - SP1 (version info will show 11.0.1).
As above person mentioned, please confirm if this is only seen with incremental backups or both incremental and full backups.
You mention technical support - please provide the case number if you have one.