I managed to get it sorted. I had issues with running RSLinx Classic. I had to kick it in the guts (Australian for ‘restart it’).
However, my setup is actually this:
Rockwell VM: running RSLinx Classic, Logix 5000 Emulate, and Ignition gateway with OPC-UA and OPC-COM modules installed (basically just using to connect locally to OPC-DA to avoid horrid DCOM config and serve up PLC tags to other remote Ignition).
Ignition VM: running full Ignition gateway. This is the Ignition gateway I actually need to be reading the PLC tags.
OK, I know what I’ve been doing wrong. I’m trying to use Ignition as a pass-through OPC-UA server for another Ignition gateway to access tags from, but confused the purpose of a remote tag provider, which is not to create tags locally, but to access them remotely via the gateway network.
I’ve resolved everything by creating an OPC-UA connection to the remote Ignition gateway’s OPC-UA server, dragged all (or most - that took a while…) of the tags from the PLC (via RSLinx - OPC-DA) into the remote Ignition tag browser, and I can now access these tags as I expect, and create new tags within my local Ignition using these tags.