When you tries to make an manual backup from VAMI or the scheduled backups have failed. The error messages in the VAMI gui when trying to do an manual backup:

Log in to the CLI with root account.

If the first run of the command outputs “Permission denied” try to restart postgres DB. See error:
sudo -u vtsdbuser pg_resetwal -f /storage/vtsdb/vtsdbdata
could not change directory to “/root”: Permission denied

Restart postgres DB
service-control –restart vmware-vpostgres

Second run.
sudo -u vtsdbuser pg_resetwal -f /storage/vtsdb/vtsdbdata

Output when command runs with success:
Write-ahead log reset

Start the services again.
service-control –restart vtsdb
service-control –restart vstats
service-control –status

Run an manual backup in the VAMI.

Links:
vstats and vtsdb service fail to start following upgrade of vCenter to 8.0.0