Google posted that they made a change to how the index coverage status report works around sites that have been migrated to the mobile-first indexing initiative. Google said now the error counts and new issues will reflect the status of mobile-first indexing. So the report will no longer show the desktop errors, but rather, the mobile errors, if your site was migrated to mobile-first indexing.

Google posted this in the data anomalies page and wrote:

This has no impact on your rankings in Google search, it is just a reporting change within that specific report in Google Search Console. Here is a screen shot showing where Google documented the change:

Forum discussion at Twitter.