Hosts in the new RESTBase Cassandra cluster are issuing WARN messages for mismatched cluster names (eqiad!=restbase):
Cluster name eqiad is legacy cluster, and restbase is the new cluster (running Cassandra 3.11.0). The message would seem to indicate that hosts in the old cluster are attempting to Gossip with hosts in the new cluster.
Upon cursory examination, the lists of seeds in both clusters seems correct, so this may be old state from a previous misconfiguration. More research is needed.