In Jive 9.0.0 only System Administrators with Full Access permissions are able to edit discussions created by other users. This is the expected behavior in Jive.
The ability to tag a piece of content also requires the same permissions as editing that content. This means that tagging another user's discussion can only be done by a user with Full Access system permissions. This behavior has changed in 9.0.1 and Cloud 2017.1 so that group or space admins can update tags.
This is a common source of confusion for group or space admins, as the permission system between Documents, Discussions, and Blogs are all slightly different.
If you are a group or space then you may see buttons to Delete or Move a discussion, but you will not be able to Edit a discussion. This is the expected behavior in Jive.
Why was this done?
Discussions do not have a versioning or history tracking system. This means that if a discussion is edited by another user, there is no history of what the changes were or who made the changes. Discussions are always assumed to be authored by the original creator, while a document will be created by a single person but may have been edited by multiple authors.
This difference in functionality between documents and discussions is a key reason why the editing functionality is also different.
If you find yourself needing to edit a discussion then that may be a signal that the content should be a document instead. You can convert a discussion to a document by clicking the "Convert to document" link in the actions list on the side of the discussion.
Changes behavior in editing tags and categories in Jive 9.0.1 and Jive Cloud 2017.1
Jive 9.0.1 and Jive Cloud 2017.1 will see a change in behavior so that social group admins and space admins will be allowed to edit tags and categories for discussions created by other users. These admin users will not be allowed to edit the content of the discussions.
Applies to Jive 7, Jive 8, Jive 9.0.0 and Jive Cloud 2016.3