Environments suddenly stopped working

I have GitLab CI jobs that have environment specified for dynamic environments. They’ve been working fine for some time, but have mysteriously stopped working, today. The CI jobs still run fine and pass, and GitLab shows that the build is created a deployment, but the Environments page always show that there are no deployments.

Does anyone have any suggestions on how to troubleshoot this? I’m at a loss on why it’s suddenly not working.