A content source that has finished processing still shows up as "Running" in the UI despite clicking Stop. This prevents processing anything else on the content source.
Add the steps involved:
View the different values for the “status” collection at MongoDB Collections Description.
You can also run a query in RoboMongo in the Content Source database to view the status of the last crawl:
Related articles appear here based on the labels you select. Click to edit the macro and add or change labels.