I just noticed some misbehaving launches of my EC2 agents in one of two configured clouds. When I opened the AWS cloud configuration, the account region was empty along with the list for the regions. since I can no longer select a region to enter, testing my account fails because the keypair is not valid for the chosen region (null).

I was running plugin version 1887 when I first noticed it and discovered there was a bug fix release a couple of days ago so I updated to 1901. So I'm not sure if there are any earlier versions that work without issue.

This was also noted in https://community.jenkins.io/t/ec2-plugin-suddenly-doesnt-keep-region/30074/2