If you're burndown chart isn't burning down, something is blocking your team. A manager finds out what is blocking the team and works on it.
If your team has a bunch of tickets in process- then your WIP is high - that's bad. Someone taking on more tickets to just get to work should be pulling the equivalent of an Andon cord.
Tasks should not have estimates - tasks should roughly have the same time to complete - a task that takes 10 days is not a single task.
A sprint meeting should only assign new tickets based off the previous rate of completion. Adding more WIP only fucks things up more than they are.
Management sees the rate of completion of features - and then calculates the time to project completion in sprints.
IF YOU HAVE A DEADLINE and you're missing it...
- cut back on features - or find out what's blocking your team.
Developers need to be told to emphasize and raise up items that are blocking them.
In any value stream - there is only one current constraint. The rest of the production process needs to be subordinated to the constraint. Is it pull request reviews? Is it the QA process? Is it ambiguous tickets? Are questions not getting answered?