Undefined index: title
I got this error because one of static pages didn't have [viewBag] section. But I think the plugin should handle the error.
I found this very helpful.
The Search Plugin was working across all my CMS pages until a day ago then it died. After fruitless attempts to fix it, I finally consulted the error logs (yes should have done that first!) and found the following 'Undefined index: title', that, after a quick online search brought me to this page and a resolution.
On one page out of 113, I found the [viewBag] and deleted it. Now everything is working fine. The problem stemmed from using the Static Pages plugin at a certain point in the development and then opting to just use the CMS Pages alone.
Live and Learn.