When using an Azure DevOps deployment pipelines with exclusive lock for a stage and triggering a deployment pipeline parallelly, only the latest deployment runs and all previous deployments that triggered automatically get cancelled. This would be fine with cumulative deployments, however, if you have a different content in each deployment run, canceling the one deployment affect the system badly due to missing updates to the system.
Following image shows, pipeline automatically cancelled the previous run and runs only the latest deployment.