The last few days i was unable to upload cover-art sometimes.
If you check: https://s3.us.archive.org/?check_limit=1&accesskey=3aMig9m2cFOXc31C
you can see total_tasks_queued and total_global_limit if total_tasks_queued is greater than total_global_limit (11999) you can’t upload.
Does this mean there are 11999 pictures in the current queue?
If that is the case there should be a problem because on these graphs:
https://musicbrainz.org/statistics/timeline/count.coverart+count.edit.type.314#r±v
you can see only 3500 art-covers is the maximum number added on one day.
If that is the case maybe someone is missusing the accesskey.
