==> /opt/neo4j-cluster/core-03/logs/neo4j.log <==
2020-05-27 11:25:35.450+0000 INFO Database 'system' is waiting for a total of 3 core members...
==> /opt/neo4j-cluster/core-03/logs/debug.log <==
2020-05-27 11:25:35.450+0000 INFO [c.n.c.d.RaftMonitor] Database 'system' is waiting for a total of 3 core members.
Thanks. I think I may have found a problem. My test hardware was a small cluster of Odroid XU4 SBC's. No good for production, but good for testing a cluster without spending too much with Amazon. This simply did not form a cluster.
But when I put together three new VM's with just Java, neo4j, and configured a cluster, this came up just fine.
So the problem is my end, and I need to rebuild my Odroid cluster (cue obligatory star wars reference: these are not the odroids you are looking for).