Delayed jobs are not being picked up by the workers

[maksimf]

Summary:

I have a few hundred tasks, just sitting there, not being picked up by any of the workers. I did check that:

• tasks are in the same queue that the workers are launched for (canvas_queue)
• workers are indeed spawned (via ps aux)

Steps to reproduce:

1. Perform any action which triggers a delayed job, like inviting new user

Expected behavior:

Email is sent

Actual behavior:

Email job is queued, but the task is not picked up by the worker (0/1 attempts)