Errors in sidekiq log: psetex not found: redis 2.6 requirements?

I am experiencing delays in update of the web app (activity page, commits, etc) since migrating to 7.14 to 8.1 two weeks ago (I updated to 8.2 today).

Looking at the jobs admin page, I can see that the jobs are queued but not executed.

Looking at Sidekiq logs, it might be the case that the problem comes from an error when executing the jobs (psetex command unknown). That command was introduced in redis 2.6.

Gitlab requires gitlab 2.4+. I have actually redis 2.4.15. Isn't it the case that gitlab 8.0 now requires redis 2.6+?

2015-11-24T12:02:19.071Z 1675 TID-ouiotkofg WARN: {:context=>"Sidetiq::Handler#dispatch"}
2015-11-24T12:02:19.073Z 1675 TID-ouiotkofg WARN: ERR unknown command 'psetex'
2015-11-24T12:02:19.073Z 1675 TID-ouiotkofg WARN: /home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/redis-3.2.1/lib/redis/pipeline.rb:83:in `finish'