Time to go back to ifconfig sit0/sit1 method it seems.
The new method doesn't work on CentOS 8.1 for neither servers, event at boot time.
Old method:
https://agora.nasqueron.org/Dwellers#No_network_at_boot_time
Files to edit:
rOPS > https://devcentral.nasqueron.org/source/operations/browse/master/roles/core/network/files/ipv6-tunnels/
Servers impacted: Dwellers, Equatower