We've been having intermittent issues with search scopes losing their items. In order to resolve the issue, I have to reset the search index and do a full crawl in order for the documents to appear. I've confirmed that the items do exist in the contentDB
but are not searchable using the specific search scope or using the All Items search scope.
I've reviewed the gatherer log. For some reason the items are being removed but the incrementals don't pick up the files nor doing a full crawl (without resetting the content index).
Has anyone had this issue before and is there a way to prevent it from happening?
You said your items was removed for some reason, but you confirmed that the items is exist in the contentDB. So, I think this is the SharePoint
search services can't work normally. So, I suggest you to restart Office SharePoint Server Search, Windows SharePoint Services search.
you can delete the items,then reset the search index and do a full crawl.