I am not able to cancel the alarms from the Pipeline
Hitting the cancel button wont do anything.
Cancellation is evaluated at the transition between pipeline blocks. It won’t stop a block mid-evaluation.
Hmm, no, some blocks also check if an event has been cancelled.
Can you get a thread dump and upload it to this post?
Sorry, I don’t see anything obviously wrong. You may need to run this through support so they can enable logging and catch it if it happens again.