I have just re-installed my VestaCP and restore all VestaCP users recently. Everything seems to be OK after restore. However, for daily backup function, one of my domain data was not included in the backup file.
And I fixed the problem by just running the following command on SSH.
v-rebuild-web-domains <user name>
After that, try to run this command to see whether is really backup successfully.
v-backup-user <user name>