SharePoint Not Crawling List or Library

SharePoint search results were not correct or would be missing some data. After hours of digging around, I noticed that one Search Scope was empty. To try and fix this, I went as far as reseting the search index, yes, clearing out all the search data. No fun!

Here is what I found to work.

List Settings
Allow items from this list to appear in search results?
Change this to NO
Run a crawl on the Content Source.
Go back to List Settings.
Allow items from this list to appear in search results?
Change this to YES
Run a crawl on the Content Source.

My Search Scope filled up.
Search was working again!