Migration instructions from 2.3 to 2.4 should include a step to set RAILS_MAX_THREADS to a value other than 1 in system-sidekiq DeploymentConfig. Ideally the value would be 25.

Since system-resque has been removed and system-sidekiq became responsible for processing all background jobs of system, no concurrency can easily lead to ActiveRecord timeouts while the ORM layer waits for a session slot to become available from the connection pool.

This was the root cause of https://issues.jboss.org/browse/THREESCALE-2285.