One team is requested to remove/delete the Release timeboxes that are no longer needed in Rally, which is over 200.
When I try to do a bulk edit for timeboxes to delete all of them - Bulk action is disabled (light grey).
Update May 2023 - Users can now bulk delete Releases.
Update 2/27/2022 - This functionality will be available soon in the new UI
The Rally page is actually working as designed. Because it can be very dangerous to delete one Release (it cannot be recovered if it is deleted) they made the decision not to have bulk delete available.
We do have an unsupported Rally application that will do this. If this application is used to delete timeboxes, they cannot be recovered if deleted accidentally. You can find the application here: https://github.com/RallyTechServices/timebox-creator