Fatal Error on multisite when network activated

My Setup:
PHP 8.4
Multisite with SUBDOMAIN_INSTALL = false

Site crashes when I activate the plugin in the network admin.
From the Error Log:

[25-Sep-2026 09:39:37 UTC] PHP Fatal error: Uncaught Error: Undefined constant "COOKIEPATH" in /wp-content/plugins/youtube-showcase/assets/ext/emd-session/includes/class-emd-wp-session.php:134
Stack trace: 0 /wp-content/plugins/youtube-showcase/assets/ext/emd-session/includes/class-emd-wp-session.php(99): EMD_WP_Session->set_cookie() 1 /wp-content/plugins/youtube-showcase/assets/ext/emd-session/includes/class-emd-wp-session.php(58): EMD_WP_Session->__construct() 2 /wp-content/plugins/youtube-showcase/assets/ext/emd-session/includes/emd-wp-session.php(119): EMD_WP_Session::get_instance() 3 /wp-includes/class-wp-hook.php(353): emd_wp_session_write_close('') 4 /wp-includes/class-wp-hook.php(377): WP_Hook->apply_filters(NULL, Array) 5 /wp-includes/plugin.php(523): WP_Hook->do_action(Array) 6 /wp-includes/load.php(1308): do_action('shutdown') 7 [internal function]: shutdown_action_hook() 8 {main}

thrown in /wp-content/plugins/youtube-showcase/assets/ext/emd-session/includes/class-emd-wp-session.php on line 134

Activating the plugin on a single site however works.

Thanks in advance for looking into this!