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:
Properties that have been migrated to mobile first indexing as part of the mobile-first indexing initiative may see a change in their index coverage status. (Migrated properties have been notified by email.) In particular, the error counts and new issues will reflect the status of mobile-first indexing. Indexed page counts are not affected by this change. This is a reporting change only; it does not reflect any changes on your site.
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.