Greetings all once again! While WooCommerce 3.6 was just launched less than a day ago, we received reports via GitHub and the Support Forums that some of the new functionality shipped in 3.6 was causing issues with some hosting environments.
As such, we have opted to revert the code that was determined to be causing issues back to the version that exists in 3.5.x. We have taken that one revision, and packaged it up in version 3.6.1 to allow sites affected to easily apply the fix.
With just one pull request shipped in this fix release, the changelog is quite short:
* Fix - Remove calls to 'header_register_callback' to prevent conflicts with some hosting providers and PHP versions.
This change will fix the issue users on WPEngine hosting were experiencing on logging in to
wp-admin, and remedy the issues reported around
add-to-cart URLs in 3.6.
Download the latest release of WooCommerce here or venture over to Dashboard → Updates to update your plugins from WordPress.