Here's the mongoid.yml file that gets loaded into my sidekiq process:

development:
clients:
default:
hosts:

• my.host.1:11000
• my.host.2:11000
  database: my_db
  options:
  read:
  mode: :secondary_preferred
  write:
  w: 1
  user: "my_user"
  password: "my_password"
  roles:
• "readWrite"
• "dbOwner"
  max_pool_size: 25
  options:
  use_utc: true

To reproduce the issue, I queue up 100 sidekiq jobs that read & write from my_db. Then I start a sidekiq server. After sidekiq boots up, there's a >50% chance that I start seeing "not authorized" errors. These errors will persist until I reboot the sidekiq server.

Switching to "auth_mech: :mongodb_cr" seems to fix the issue.