Google posted that there was a data logging issue with Google Discover traffic and Google Search Console. Because of that, Google performance reports for Discover traffic starting on May 12th through May 15th. Google said "you might see a significant drop in Discover reporting."
Google is working on fixing the issue, it is unclear if the fix will bring back in data that was lost or if that data is lost forver.
Google wrote on the data anomalies page "Due to internal logging issues, you might see a significant drop in Discover reporting. Please note that this does not reflect any user-facing changes for your site, only the data reporting in Search Console. We hope to fix this issue soon."
Keep this in mind if you have any reporting to do for clients or your own internal reporting. So any data you see between May 12th and May 15th in the Google Search Console Performance Discover report may be wrong.
Forum discussion at Twitter.
