SQL server on a domain controller does not handle file deletion. How to get around?

Question

Active Directory

There is a machine, it has Windows Server 2012R2, the AD DS role is deployed, SQL Server 2012R2 Standard is installed. In SSMS, I set up a backup plan to "back up, delete old backups." After a few weeks, I found that the old backups are not deleted. There are suddenly interesting messages in the logs:
MSSQLSERVER 17052: Severity: 16 error:18456, OS: 18456[Microsoft][SQL Server Native Client 11.0][SQL Server]Login failed for user 'DOMAIN\mssql_srv'.
MSSQLSERVER 18456: Login failed for user 'DOMAIN\mssql_srv'. Reason: Could not find a login matching the name provided. [CLIENT: 192.168.х.х]
At the same time, the service of SQL Server itself is running under the user, i.e. name resolution shouldn't be a problem. Question - where to dig? The entire domain consists of this one server.
PS: A couple of messages per file - this is the most impressive thing. That is, the server receives a list of files, then for some reason in a separate connection it tries to delete them, via the connection to the FILE !!! And every time it catches the same error. What is this strange behavior? Of course, I can get around - writing a script that deletes old files from the directory is not a problem at all, but why doesn't the regular procedure work? The role of the DC is after all warning and not error, i.e. may create obstacles, but is not an obstacle in itself.

Answer 1

The service operates on its own behalf. For example, SYSTEM
And on the sql server for such a "user" there is no mapping and rights ...

Answer 2

Set the same username for the MSSQL Server Agent service.