Thank you both,
Perhaps what happened is shortly after you started using the HG612, something at the exchange detected the HG612 with PhyR enabled, and so decided to use PhyR. Perhaps it was a bit like how the FTTC DLM will only switch on upstream G.INP a little while after it detects you are using a compatible modem. That's why I suggested you might be able to get rid of it by leaving an incompatible modem connected for a while. After all, the DG834v2 is also pretty old and doesn't support PhyR, yet it managed to establish a connection. Or perhaps some software at the exchange was updated or some configuration changed and PhyR has been activated completely by accident.
This can make sense to me: If I recall right the DG834v2 doesn't do INP, so it is not processing any headers/code that the DLM is sending over, doesn't get confused and manages to pick up a DSL connection. The 2WIRE is doing some kind of INP, so it tries to process whatever proprietary code the exchange Broadcom chipset is sending, but it chokes at it and can't establish a DLM handshake successfully.
While I was fighting with the 2WIRE I left it online for more than 30 minutes, but it was not able to connect. Perhaps I should have first shut down the HG612, wait for an hour or more and then try to connect with the 2WIRE. What I also did not try is to start a line retraining period, which would probably flush any settings out of DLM's memory and start afresh with whichever CPE would be online at the time.
I am unsure what happens with Interleaving and if it is switched off when the Broadcom PhyR has been enabled. As I mentioned Interleaving is shown set as auto in the ISP's control panel and also the HG612 shows:
MSGc: 52 12
B: 118 62
M: 2 1
T: 3 2
R: 14 10
S: 0.7328 1.8718
L: 2751 312
D: 2 16
Where I understand "D" is for Interleaving?
However, when the 2WIRE was in use I would used to have double the RTT when I pinged a target or pinged my IP remotely. With the HG612 the latency is significantly lower. I am guessing therefore that the Interleaving has been switched off, or how else would I be getting reduced ping times?
Does AAISP make it clear if they are using TT or BTw for your backhaul?
There's only BTw up here, a small Market 1 exchange. I checked with the ISP too and they confirmed it.
^ This is still playing on my mind.. although I would guess its far more likely to be migration from IPSC to WMBC.
Well, when a test is triggered by user or tech staff action, a bubble shows up on the graphs of the control panel, indicating the timeline when test was executed and who triggered it. When I asked my ISP I was told that it is probably related to BT testing and I could ignore it.
Regarding INP on 2WIRE modems, I vaguely recall INP also showing on ADSLMax, but I can't recall what the values were.
I'm going to leave the HG612 on for now and not interfere with it, to see at what speed it settles and if disconnections reduce.