Memcached doesn’t work on multisite

Yes, it is deliberatelly disabled for multisite because they consume its memory pool too fast usually. If you want, you can enable memcached manually using this dropin only changing the connection port to the one, provided to you by cPanel:

https://ww.wp.xz.cn/plugins/memcached-redux/

We’re working on a proper integration for the upcoming major update of the plugin.