Did you know that you can define the concurrence rules for the events that are based on Jira dates sources?
To do that open a Jira dates source configuration and select one of the options.
By default, concurrent events are allowed.
“Don't allow concurrent events” means, as it says, the concurrent events are not allowed
“Don't allow concurrent events on assignee level” means that concurrent events are allowed as long as the events' assignee differs