I believe this is similar to (and possibly identical to but I can't tell) BAM-14857 and BAM-17463 in that it is about task configuration, etc. not getting updated immediately.

If you have a deployment with an Artifact Downloader task configured to download a specific artifact from the linked build plan and then clone the deployment the cloned deployment reverts to showing 'All Artifacts' instead of the selected artifact and the deployment does not work (it stalls and when you manually stop it it then reports that it couldn't download the artifact).

If you edit the deployment environment and re-select the desired artifact (even if it is the same artifact as was originally configured) that seems to update some internal data that allows the download to work when the deployment is next attempted.