Google has updated its data anomalies page to document that there was data loss within the Google Search Console tool for new users who signed up between June 21 and July 10, 2017.
Those webmasters and SEOs who signed up to the Google Search Console and verified properties will not see those 20 days of data. Google seems to have fixed the issue going forward, but anyone who signed up as a new user to the Google Search Console during that date range of June 21 to July 10 will be missing data between those dates.
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.
This does not impact those who signed up to the Search Console before or after those dates.