I am unable to edit theme files. Each time I try to save a file an error comes up: "Unable to communicate back with site to check for fatal errors, so the PHP change was reverted. You will need to upload your PHP file change by some other means, such as by using SFTP.".
To troubleshoot the problem all plugins were disabled, SSL was enabled, but still no luck. However, files in any inactive theme can be edited. The problem only affects active theme.
File wp-admin/includes/file.php contains the following line twice:
$r = wp_remote_get( $url, compact( 'cookies', 'headers', 'timeout', 'sslverify' ) );