Why is sending email notifications from the Gitlab server not working?

Question

Ruby on Rails

There is a server with Ubuntu, which has Gitlab 6.2.4, installed according to the instructions from installation.md. Sending email is configured via smtp via gmail.
The problem is that emails are not sent at all. In the admin panel, in the Background Jobs section, there are a large number of tasks to send, but they all lead to nothing. There are WARNs in log/sidekiq.log about "Couldn't find User with id=15", but, as I understand it, this should not lead to the impossibility of sending emails at all as such and is associated with this bug.
There is a suspicion that this is somehow related to the fact that Resque does not pick up tasks to be sent. Here is the code:

sudo -u git bundle exec rake environment jobs:work RAILS_ENV=production PIDFILE=./resque.pid QUEUE=runner

leads to this error:

rake aborted!
Don't know how to build task 'jobs:work'

What is strange, there is no resque_worker.pid file in tmp/pids/, although, as I understand it, it should be there.
There are no errors in other logs.
Judging by the fact that even if the username/password is deliberately set incorrectly in the email configuration, there will be no errors - the emails do not even try to send.
How to start emails? Where to dig, how to fix?