When is a bug not a bug? When it is a feature!
Google has just updated their data anomalies page to clarify that the earlier reported bug that had affected the average position metric, was not a bug after all.
So it turns out, the bug was, in fact, an incremental improvement in their logging system. In Google’s words:
An incremental improvement in Google’s logging system now provides better accounting for results in lower positions. This change might cause increase in impressions, but also a decrease in average positions. This change only effects [sic] Search Console reporting, not your actual performance on Google Search.
No actual ranking changes have happened to the average position metric, just the way the Google accounts for the positions.