Recently, our two 2012 DCs started logging these warnings in the System log...
No suitable default server credential exists on this system. This will prevent server applications that expect to make use of the system default credentials from accepting SSL connections. An example of such an application is the directory server. Applications that manage their own credentials, such as the internet information server, are not affected by this.
One of the DCs gets them more frequently. Sometimes it logs dozens per hour. This just started happening a few weeks back. What suddenly caused these to appear and how do stop them?