Paperless-ngx Celery won't consume documents

When running Paperless-ngx I ran into a problem where the Celery process in Docker (as part of supervisord) would start, supervisor would report it running, but the Celery process appeared to do nothing.

The last related lines I would see were:

INFO success: celery entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
[INFO] [] Adding [REDACTED] to the task queue.

I'm not sure what part of Celery does this, maybe it's just Paperless? But eventually I found a .__celery.lock file in the Paperless data directory. Removing that allowed everything to work again.

This was likely caused with Nomad terminating the process and the lock file not getting cleaned up. I now have my Nomad job remove .*.lock files before starting Paperless.