At the start of a new month, rightsizing may not display due to data not being available yet as 48 hours worth of data is required. 

This is due to a delay in CloudHealth receiving the finalized data to ingest into the reports.  It generally takes 48 hours to gather metrics for rightsizing reports.  You can select the previous month from the 'Period' dropdown to see the previous month rightsizing until data becomes available for the current month.