Discussion link not showing

The "Discussion" tab only displays if there is a discussion thread associated with the item. For existing items, you will have to manually associate an existing discussion thread (or create a new thread and associate it with). NEW Items will have discussion threads automatically created for them (if you have a designated forum set for that specific category).

There is a Permission setting for being able to associate a thread. This is a moderator permission. To associate an existing thread to a showcase item, you write down the ID of the thread, edit the item, add the thread ID into the form and hit save. Once you do that, the discussion thread is now associated with that item.

 

I can't say as reverting/merging is a core xenforo function. I've only ran into a similar issue once and that was with xenporta and a modified template in a child style (but not modified in the parent). Core XF didn't pick up the edit in the child style cause the parent was not modified.

If you have more than one style, it might be good to just check them to make sure there are not others that need reverting as well. I can help out if needed