Redundancy and Modbus Connection Issues

Running Ignition 8.1.25 with redundancy enabled. Both servers are headless linux.
Redundancy is cold & partial.

I have a myriad of devices connected (~60), most are modbus, with a half dozen DNP3.

When I perform a failover, the backup server does not successfully connect to any devices. The connected devices list would indicate they are connected, but inspecting the connections device side, there are no packets being sent (modbus) or packets slow to a crawl at 1 in 5sec (DNP3), which without history is as good as disconnected anyway and the data turns stale/bad.

The log on the backup is filled with SocketIODelegate faults, for example: End of stream reached.
at java.base/ Source)

I try reset the connection from the device end, but Ignition never re-initiates.

The "End of stream" tells me that this is a modbus device closing the connection, which indicates in turn that the primary never let go of it completely?

Backup server pre-fail over:

Backup server post-fail over

In opposition to the above, the device side of those modbus connections indicates disconnected and no packets are being sent. The tag browser also indicates bad data.

Edit: I should add.. if I fail 'back' and assume control on the primary.. all of the connections resume and everything is ok!

Hmmm. I can't help you with the IA driver (and I suspect you need to call support), but I'd be curious what you get if you substitute my alternate driver. Perhaps in parallel with some extra tags to not disturb your production kit.

It's a totally different code base, so if mine does the same, it probably isn't a problem inside Ignition.