Sometimes when running a workflow a single task will appear to have completed (there are stderr and stdout) but firecloud doesn't register the job as finished. The timing diagram will show it still "running" for hours. Usually this issue goes away if cromwell is restarted. My general workaround is to rerun the entire workflow and it usually gets through the "stuck" spot just fine.
As a somewhat similar example I attempted to abort one of these workflows and it seems to still be stuck:
https://portal.firecloud.org/#workspaces/broad-firecloud-dsde:Tumor_Only/Monitor/65c7b549-0633-4ab1-8c05-81bc1ca9073d