To see which errors are preventing documents from being indexed successfully, use the eDiscovery Exception Report to view all document extraction errors for failed items of a particular search engine.
From the Web Console, navigate to the eDiscovery Exception Report.
Click the Search Engine you want to view.
Click the Exception section of the pie chart.
The pie chart automatically updates, and an Error list appears for the selected data.
You can click either the pie chart section or the description in the graph key to make your selection. It might take a few seconds for the pie chart to update, depending on the amount of data in your report.