New innodb mysql instance fails to go online

[Peter Hutchison]

I am trying to re-add an instance of Mysql 8.0.16 server to my mysql innodb cluster.

I created the relevant users on the instance first with all privileges. I have root@localhost, root@servername, cluadmin@servername, cluadmin@subnet\subnetmask.

I have to run 'reset master' and 'flush logs' on the new mysql instance otherwise it fails to add to the cluster.

On the main instance, I open mysql shell:
var cl = dba.getCluster();
cl.status();
cl.addInstance('cluadmin@servername:3306') - Server successfully added
cl.status();

It's status changes to 'RECOVERING' and then fails as 'MISSING', it try using dba.rejoinInstance() to try to fix it with no luck. A rescan and addInstance() also fails.

Log says:
2019-07-03T10:53:11.266932Z 0 [Warning] [MY-011499] [Repl] Plugin group_replication reported: 'Members removed from the group: servername:3306'

Configuration is correct
No other information given on why it fails to join up.
The mysql error.log on the server instance is empty!

Any ideas why and what to look for, or is Mysql Innodb cluster is just rubbish?