The page Processing Queue shows the current state of document processing for your uploads. The page currently only shows at most the 80 newest jobs. There is a maximum of 40 done jobs (successful, cancelled or failed) and 40 not done jobs.
The sidebar lets you filter for a specific job state. The Currently Running tab shows all jobs that are currently executing and their log output. The page refreshes 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 first enters "stuck" state and 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.