The supposed reason is that the agent did not have a chance to report to TMDB after PhEDEx upgrade.
Such behavior is confusing to the transfer team. It may also hide problems from the Computing Shift Person, who are watching this table for the agents that are down.
Long existing node was found not to show in the nodes/agents table: https://cmsweb.cern.ch/phedex/prod/Components::Status Also the Data Service agents API did not show this node at that time.
The supposed reason is that the agent did not have a chance to report to TMDB after PhEDEx upgrade. Such behavior is confusing to the transfer team. It may also hide problems from the Computing Shift Person, who are watching this table for the agents that are down.
Unfortunately PhEDEx does not keep a history of the agents "down times", see: https://github.com/dmwm/PHEDEX/issues/313
Check in which situations agents are not listed, and whether this is a bug or a feature.