Symptoms

WordPress plugins marked as Inactive for WordPress Multisite instance. If select several plugins and activate them Plesk reports that it is enabled. However, next attempt to open Plugins pop-up shows that it is still in Inactive status.

In WordPress Multisite admin panel on the network level it can be observed that plugin is enabled and has Network Activated status

The following entry in Plesk /usr/local/psa/admin/log/panel.log with debug mode enabled:

Warning: Plugin '<plugin_name>' is already network active.

Cause

Plesk WordPress Toolkit manages only plugins for main site of WordPress Multiserver.

Resolution

It is an expected behavior and this status can be ignored since plugin is enabled on network level.