This is now resolved.

We're still fully investigating the root cause but there was too much activity with etcd and clean up not happening fast enough. This caused downstream impacts on pods piling up and Kubernetes API rate limits being hit. There were Out Of Memory issues because of this.

Our older Digital Ocean cluster is doing far higher volume that this so we need to determine what configuration is different and making appropriate changes to prevent this happening again.

Our new EU region isn't dequeuing runs, we're working on a fix now.