We have 3 content sources, 2 are for SharePoint sites and one for SharePoint profiles. if we start a full crawl on one content source at a time, crawl ends without issues. But when full crawl is started on more than one content source, those crawls never end (even for the incremental). We removed and created the search service application many times, but the problem persists. And when we try to start the search crawls one by one, it never stops, it seems like something is broken and could not be repaired.
In fact, the crawl component is gathering items, and we checked this in the local temp gatherer location, files are being downloaded, but it seems like it Content Processing Component is not processing items, due a communication error or something else, as described by the crawl load report.