Subscribe problem using multiple OPCUA Interfaces

Our physical machine is made up of multiple OPCUA servers. 

In our Unity scene we have several OPCUA_Interface objects to connect to each server and a OPCUA Node connected to each interface.

If we use Read Value on the nodes we get the values we expect, however if we use the subscribe option we get the same value across all interfaces as if they are being overwritten somehow. We can get around it by using Read Value but it seems to come with a heavy performance cost. 

Is this a bug or is there another way to set this up?

Many thanks