pg_ctl restart does not unregister itself from GTM. After restart, coordinator/datanode does not remember it is registered and again tries to register itself to GTM, then fail and all the node fails. Pg_ctl restart should unregister itself from GTM. This bug is in all the versions of XC.
At present, GTM client library (libgtmclient.a) provides API to unregister such nodes. Applications can build utility for this purpose. Pgxc_ctl (Koichi's private project now) may provide this capability.
This will be moved to feature requests.