Ignition redundancy is both latency sensitive and subject to split brain syndrome. If the comms goes down between sites, both servers will end up active and therefore numerous properties start to diverge.
So let me amend my answer to:
Ignition redundant servers must be installed on a common LAN with a robust network layout (preferably multi-path, like RTSP), such that any loss of comms also results in loss of comms to all clients and all devices and all databases. (Trunk port for multiple VLANs, or multiple trunk ports with RTSP and all VLANs on all ports.)