This is an unusual misstep from search giant Google.
Google has announced (via their data anomalies page) that users who have signed up for Google Search Console between the dates of June 21 and July 10 2017 could have lost up to 20 days worth of data. If you signed up outside of those dates, you will not be affected (phew).
The hole has now been fixed and everything should be running as normal. However, that data is long gone and anyone affected by the bug, will not see any data for those date ranges.
In Google’s words:
All first-time Search Console users who joined Search Console during this period will be missing site data during this period. First-time users who joined before or after this period are not affected.