Win32_ShadowCopy.Create method only accepts ClientAccessible and NASRollback context. Does not accept All, AppRollback, Backup, FileShareBackup context.
As a result, if the backup script crashes, the shadow copy is not removed, and causes data loss. When the Jenkins job was stuck and I had to abort it, the Jenkins log file was filled with zeroes after a certain point.
Find a goddamn workaround.