System Log Error will periodically throw these errors:

This is under System Logs>Errors and filter on message contains ecc_agent_status.  Note that em.sm.mid would be different a value or values in your case as this refers to MID Server name/s existing in your instance.

All current supported releases up to London version.

There is a missing ecc_agent_status record in your instance.  For each MID Server existing in your instance, there should be one corresponding ecc_agent_status record. This record can be deleted or may not have been created for some reason or another.

The most likely cause is PRB1287729 related to Clone Exclude/Preserve settings, and so is usually see on sub-production instances.

The recommended solution is to re-clone after upgrading to Madrid, or after implementing the workarounds in:
KB0688954 / PRB1287729 The MID Server Exclude/Preserve Clone settings cause MID Server issues on the target

If that is not possible at the time, Log in as admin in your instance and on filter navigation, enter ecc_agent_status.list. For each MID Server missing from the list, click "New" to create a new record and then enter the corresponding MID Server Name then save the record. The other fields will be automatically populated usually within 10 minutes.

The ecc_agent_status record is created via out-of-the-box Business Rule "Insert into MID Server Status".  The Business Rule will create one ecc_agent_status record once a MID Server record is created in your instance. Check that the Business rule exists and is active.  In the MID Server>Dashboard.  The ecc_agent_status records are displayed in the top most widget.  Please refer to our product documentation for more information.