Sometime while trying to delete a pipeline or workflow you might get an error as below and that doesn’t allow you to delete the workflow/pipeline
Pipeline:[pipeline_name] couldn't be deleted. Reason: Pipeline execution is in progress.
Although when you try looking for execution in Deployment tab you are unable to find any running/paused execution.
Reason: Most common reason for this behaviour is there might be any old deployment which got stuck or went in bad state and status of that deployment is in either pending/queued etc.
So in that case most probably those executions are 3 month older and thats why not showing up in deployment page as by default it applies 3 month filter so in that case you can manually apply the date filter for previous month and it should show up the deployment.