So. Much. Networking. LLAPI? HLAPI? Community Edition HLAPI? MLAPI?
Am back to using the LLAPI with some handy wrapper code based on Lina Adkin's UnetLLAPIWrapper - https://github.com/LinaAdkins/UnetLLAPIWrapper. For NAT/Connectivity issues am trying out the MLAPI.Relay project. A Unity Relay Proxy replacement - https://github.com/MidLevel/MLAPI.Relay . So far so good... Cautiously optimistic...