MSSQLSERVER Login failed for user '' after upgrade

In our case, both servers are running on Windows Server 2012. And we’re running Microsoft SQL Server 2014 (SP3) (12.0.6433.1) - Enterprise Edition.

But I’m upgrading to Check_MK 2.0.0p4 and a quick glance at the release notes showed some changes to the MSSQL agent if I’m not mistaken. I’ll see if that one works.