Error notification

For site https://www.schadeck.eu

• Error Level: E_ERROR
• Message: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function “shift8_cdn_uninstall_hook” not found or invalid function name in /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/class-wp-hook.php:324
  Stack trace:
  #0 /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
  #1 /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
  #2 /var/www/vhosts/schadeck.eu/httpdocs/wp-admin/includes/plugin.php(1269): do_action()
  #3 /var/www/vhosts/schadeck.eu/httpdocs/wp-admin/includes/plugin.php(960): uninstall_plugin()
  #4 /var/www/vhosts/schadeck.eu/httpdocs/wp-admin/includes/ajax-actions.php(4748): delete_plugins()
  #5 /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/class-wp-hook.php(324): wp_ajax_delete_plugin()
  #6 /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
  #7 /var/www/vhosts/schadeck.eu/httpdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
  #8 /var/www/vhosts/schadeck.eu/httpdocs/wp-admin/admin-ajax.php(188): do_action()
  #9 {main}
  thrown
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