We got this feedback from support, which I’m happy to share:
It looks like this unexpected behaviour was caused by a known bug in the Nomad autoscaler service we use to autoscale Nomad-based apps. This bug causes the service to freeze up requiring a manual restart, and has happened to our platform only a few times over the last year. We’re assessing the alerting we have set up on the autoscaler service so that we can catch these faster in future, preventing this situation.
We’ve restarted the service so autoscaling should be working properly again. Sorry for the inconvenience