The page Processing Queue shows the current state of document processing for your uploads.
At the top of the page a list of running jobs is shown. Below that, the left column shows jobs that wait to be picked up by the job executor. On the right are finished jobs. The number of finished jobs is cut to some maximum and is also restricted by a date range. The page refreshes itself automatically to show the progress.
You can cancel running jobs or remove waiting ones from the queue. If you click on the small file symbol on finished jobs, you can inspect its log messages again. A running job displays the job executor id that executes the job.
The jobs listed here are all long-running tasks for your collective. Most of the time it executes the document processing tasks. But user defined tasks, like "import mailbox", are also visible here.
Since job executors are shared among all collectives, it may happen that a job is some time waiting until it is picked up by a job executor. You can always start more job executors to help out.
If a job fails, it is retried after some time. Only if it fails too often (can be configured), it then is finished with failed state.
For the document-processing task, if processing finally fails or a job is cancelled, the item is still created, just without suggestions.