That implies that hostname -f is returning xc4elogin1 but that name isn’t valid on the other hosts.
(See Https messaging fails, communication error between HPC and cylc hosts - #3 by oliver.sanders)
You can hardwire the name in the global config but that then limits you to always running on that host. You can also try using IP addresses instead of host names.
See Global Configuration — Cylc 8.0rc1 documentation
Alternatively you can configure which hosts you want the scheduler to run on and only choose ones which don’t suffer this problem: Global Configuration — Cylc 8.0rc1 documentation