I couldn't find a Category and Forum specific to Azure AD Connect, so please feel free to move this post, if it is the wrong location.
The issue is as described: Azure AD Connect is attempting to connect to its configured SQL Instance using machine account of the server on which it is installed in addition to its gMSA. The service is working using gMSA, and is otherwise synchronising, but the additional connection attempts using the machine account are obviously generating errors on SQL Server as well, as the machine account is not permitted access to the instance.
Stopping the "Microsoft Azure AD Sync" service stops further errors being generated, so it's definitely Azure AD Connect doing it, but it clearly shouldn't be.
Has anyone else encountered this?