We have been seeing an increased amount of customers reporting that Google WebMaster says that GoogleBot “Cannot Access CSS & JS”. This is due to a robot.txt file on the customers site blocking GoogleBot from accessing /wp-admin/ and /wp-includes/ which can be added through a plugin or a custom created robot.txt file.
To solve, you will need to remove wp-admin and wp-includes from being blocked in your robot.txt file. We have created a Support Garage Article to walk you through reading and modifying your robot.txt file.
For more information on why unblocking wp-includes and wp-admin in your robot.txt file is safe, visit https://yoast.com/wordpress-robots-txt-example/#updates