The last 6 months of data is being truncated on the first day of the month.
Aria Operations 8.x
The value of the setting 'Time Series Data Retention' in the 'Global Settings' menu determines how long metrics are retained and when it should be truncated.
If the value is set to 1 month, then data older than that will be truncated.
If there is a value set for ' Additional Time Series Retention' then the data will be rolled up to 1-hour interval data points for that period of time.
Change the value of 'Time Series Data Retention' to reflect your business needs.
More information about 'Time Series Data Retention' & 'Additional Time Series Retention' can be found on the Broadcom techdocs site.