I created a content type Event.Added user entity reference field(organizers) in it so that users related to the event can be tagged or referenced by the content author.After that I created an Event and tagged the user related to the event using user entity reference field.
Now users who are tagged in the event are able to edit the content in which they are tagged or referenced.Even if they are not the author of the node.

Tried to rebuild the permisssion but same problem.
In my website i have set the permission so that user may able to edit & delete only content they own.