SqlServerWriter is missing from:
vssadmin list writers
Eventlog contains SQLWRITER error with ID 24581.
Sqllib error: System table sys.sysdatabases in SQL Server instance SERVER\SQLDB is empty.
Open Microsoft SQL Server Management Studio, connect to the database and click: New Query
use master go sp_addsrvrolemember 'NT AUTHORITY\SYSTEM','sysadmin' go
Click: Execute (F5) and after that restart services from PowerShell:
Restart-Service SQLWriter -Force Restart-Service "Backup Service Controller" -Force