The RESTBase Cassandra cluster has some nodes where Prometheus metrics (those that come from the JMX exporter), are missing.
For the machines affected, executing curl against the exporter URL just hangs indefinitely. I attempted to restart 1011-a to no avail. I then live-hacked cassandra-env.sh to roll back the exporter jar to the 0.8 version we used before, and it is now working. More investigation is needed.