The data_engine probe would not stay up and running and the log showed errors indicating that the CM_METRIC_UNIT table was missing.
Aug 21 10:03:11:330  de: [QoSData] ExecuteRecords - 1 errors
Aug 21 10:03:11:330  de: (1) ExecuteRecords [Microsoft OLE DB Provider for SQL Server] Invalid object name 'CM_METRIC_UNIT'.
Aug 21 10:06:11:456  de: COM Error [0x80040e37] IDispatch error #3127 - [Microsoft OLE DB Provider for SQL Server] Invalid object name 'CM_METRIC_UNIT'.
- UIM 8.4
- data_engine v8.4
- Suspect either a deletion of tables or restore from backup that did not complete properly due to the number of missing tables in the database schema.
Reran the UIM installation to repair the schema which was missing many tables, including many CM_* tables then the data)engine started without issue and the error subsided.