This plugin’s configuration section, within the “Manage → System Configuration” area of Jenkins, has a bug that wipes the Alternate EC2 url and region parameters. In the event that someone opens the System Configuration page and performs a “Save” without resetting these fields, Jenkins will get into a state where it’s either partially or completely unusable due to it saving a configuration with no region set, which shouldn't be allowed.
Attached are two examples of what has happened when a save occurs and the fields were not set.
Additionally, when you go to the configuration page and try to reset the fields an error is returned via the plugin, and saving still results in the region not being set. A screenshot of that is included as well.
If you wait long enough, eventually the plugin will return a 504 gateway timeout. A screenshot of that is also included.
In order to resolve the issue, we have to go onto the ec2 instance where jenkins is running, edit the config.xml and restart the jenkins docker container.
Edit: We have since updated Jenkins to v 2.204.2 and the issue persists.