Yesterday afternoon Google temporarily disabled the ability to validate fixes for issues in the coverage report. This is related to some “minor updates” the Google Search Console is adding to those coverage reports over “the next few days.”
Here is a screenshot of the notice, and you can see the “validate fix” button is grayed out and disabled.
As you can see, the message reads “Limited functionality: We are making some minor updates in the next few days. During this period you will not be able to issue new validation requests.“
“We’re preparing to migrate all Search Console properties to the updated item classification in approximately 2 weeks. In order to do it smoothly, we are going to disable task validation of index coverage issues until we finish the migration. Thanks for your understanding” – Google search Central official Twitter stated the answer.
Google later on in the day explained this is being temporarily disabled because of the classification changes they announced in mid-June to the Search Console reports.