The user created a disk group, but forgot to make it shared. After it was made a shared disk group, the user attempted to start the second node (which had not been rebooted). pdbadmin start node on second pdb node failed with this repeated message until it finally timed out:
return from cluster_establish is join not allowed now retrying cluster_establish
You can either reboot the second node or run vxdctl enable.
pdbadmin start node now works.