Admin users on domain separated instances with domain delegated administration enabled can see the following when trying to install a plugin although no plugin is currently being installed:
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When 'Domain delegated administration' is enabled the user must comply with the following constraints in order to activate plugins:
If the 'Domain delegated administration' property is set to true, make sure that the administrative user is in the 'global' domain.
PRB1363926 is currently being reviewed to correct the message