wp-admin/admin-ajax.php Error 400 Google search console.

Where are you seeing this error exactly?

https://drive.google.com/open?id=1XqnS7xXpiGvuYCwhFv1H84CJWmaJOuTH

Please look on the picture.

Thanks.

Not sure why Google is trying to access that file. The error is correct, and it shouldn't be accessible.

Perhaps you have a plugin calling it on your front end somewhere? GeneratePress itself only using AJAX in the Dashboard.