Many webmasters are noticing that the Index Status report within the Google Search Console is showing a significant drop between August 16th and August 23rd. Meaning, the pages Google has indexed on your site has dropped.
The good news is that every webmaster seems to be impacted by this. So this is likely a reporting glitch or change in how Google reports indexed URLs in the Index Status report.
Here are several charts all showing a dip in index count after August 16th:
I assume this is a reporting glitch and will be resolved eventually.