Well if you want to take the Asus as an example G.INP appears to be working in Italy, in Australia, in the UK with Huawei cabinets but not at all against a brand new implementation on ECI cabinets - what are the odds the cabinet isn't the problem?
Who knows? Without putting much effort into it, I can come up with 16 fundamentally different framing setups on the wire. The Asus/Huawei combination would seem to prove one of those combinations, leaving another 15 to go. If the blame could be apportioned 50:50, then a 50:50 chance over 15/16 scenarios leaves you at odds of 47:53.
If the Asus is working in Australian VDSL2 deployments, it is likely to be working with Alcatel-Lucent DSLAMs, which could well be an entirely different setup.
I'm sure that both pieces of equipment will have been through testing - but I'd be a liar if I thought that the Asus had been through anything like the rigorous testing that a telco would insist on for network equipment. Can we really say it is likely to be 50:50? I don't know.
The fact is that these are complicated pieces of kit, and being shown to work in one narrow way usually leaves plenty of other options to go wrong.
However, with @ejs finding a firmware update from Asus making reference to changes for the ECI DSLAM, I'd say it stacks the odds in one direction somewhat.
I've spent most of my professional career chasing and fixing bugs in interworking between telco equipment. If I started out with the certainty you do over the source of a problem, I wouldn't have solved anywhere near as many problems.
Regardless they shouldn't have rolled out without testing against all modems users might reasonably be expected to be using, you know like ones they sell in the BT Shop, and Currys and Tesco FFS.
Why? They have a properly-placed requirement that modems must have gone through conformance testing before being allowed on the network. Should that be just thrown away? Ignored?
And according to to list you posted here http://forum.kitz.co.uk/index.php?topic=17086.0
Neither has any TP-Link, Netgear, Linksys, or Trendnet model all of which can be purchased from the BT Shop.
Ability to buy is not the same as being allowed to use.
And all are likely to also support other modes where they can be used: ADSL and PPPoE modes.