What do you mean by exactly by “concurrency” issue? Can you please elaborate? What is happening out of order exactly?
A sidekiq job being added to a queue does not guarantee overall order of execution as there are different queues with different priority so some jobs can get ahead of others.
Also “skipping code execution”. Can you elaborate? What code? When a job runs the code will not be skipped. Have you checked your /logs that nothing is breaking?
And be aware you might be running an unsupported install which might be at the root of your issues …