Whenever you see "(hidden)" in your company Pipedrive account, it means that you do not have the necessary permission or visibility to view that specific item.
If you do not have permission to view an item linked to a deal, you will see this reflected at the top of any item's Detail view.
You will also see the item marked as hidden if you apply the column in the List view.
Why are items shown as hidden?
There could be a number of reasons items in your account are appearing as hidden:
You can see some more information regarding why you can not view the item in the sidebar of the Detail view.
We suggest speaking to the Admin User of your Pipedrive account if you need to have this permission or visibility adjusted. In order for your admin user to make the necessary changes, they should go to Settings > Manage Users.