FWIW, it also seems that users with unlocked HG612s, but with older firmware versions & remote BTOR updates blocked are seeing similar issues as soon as G.INP is activated at their Huawei cabinet DSLAM.
i.e. The modem will sync, but at a quite heavily interleaved depth & thus reduced sync speeds.
The 'fix' appears to be upgrade the HG612 to the latest firmware version which does appear to be G.INP ready.
I have never blocked BTOR updates on my HG612 & despite losing the GUI (which I don't personally need), the transition to G.INP was very smooth/instant.
I haven't seen much in the way of improved speeds etc. but my connection does still appear to be capped at 22.4Mbps/5Mbps sync speeds, no doubt due to crosstalk over 1100m or so of copper.
However, I do now see incredibly few error seconds and incredibly few CRCs.
However, due to the low levels of interleaving now applied to my previously fast path connection, I do see a fair few FEC, the 'new' LEFTRS, rtx_tx, rtx_c & an occasional rtx_uc counts.
There is quite a difference between Line Attenuation & Signal attenuation, but nobody seems able/willing to tell me whether that is due to perhaps being on a 'stable' profile or not.
Maybe DLM will relent in due course?