Can't update theme option in X theme latest version

[zenchange]

Error comes when I try to edit theme option - The preview could not load due to the iframe response being incomplete. This is most often related to a plugin conflict, or customizations introducing a PHP error.

Also wp admin logout itself with this error - Your session has expired. Please log in to continue where you left off.

[rad]

Hi Zen,

Thanks for reaching out.

Would you mind providing your FTP login credentials as well? Or please try adding this line to your child theme’s functions.php

add_filter( 'nonce_life', function () { return 4 * HOUR_IN_SECONDS; } );

The reason for that is heartbeat nonce or ajax nonce is regenerated to another and fails to verify. Please check this related thread as well Cant Save changes

Thanks!