It seems that the Google Search Console seems to be experiencing a bug in their Search Analytics report.  More specifically, the bug is with the average position metric.

There are several webmasters who claim that the average position metric on the search analytics report took a sharp dive since July 13.  There have been several screen shots taken from various webmasters who have shown proof of this decline.

The following screenshot shows the green line dropping significantly, where the line represents the average position data:

In the end, don’t worry about it, as many webmasters are having the same issue.

Source –