The hourly aggregation always starts processing defects from Dec 5, 2017 11:00 onwards.
Currently there are no defects in database, so it always ends with 0 rows.
The aggregation process had stopped around the time of the error. The cause of that was not investigated but can relate to prolonged loss of connectivity to database.
The point at which aggregation stopped can be checked by running queries on the database
Was detected in APM 9.7
If there is a concern about the data, a support case should be opened with the following information
Logs from all Enterprise Managers in the cluster
A backup of the APM database if possible, otherwise output of these tables:
and output of the two select statements listed in the document