. . . after all, you are not a "newcomer" but a regular contributing member.
I consider myself a lurker as opposed to a regular contributing member. I am only posting here because I asked on this forum and people took the time to look into it and answer it, so I can only do the same.
Though I am afraid of being incorrect.
. . .
I beta tested the TD-W9980 before it was released for sale in the UK. One of the things I immediately highlighted to them was degradation of SNRM due to bit swap.
. . .
The main difference here is the difference of chipset, although I imagine that you are fully aware that the TD-W99
80 has a Lantiq chipset while the TD-W99
70 has Broadcom.
Perhaps it’s the implementation (such as configurable variables that TP-Link can make) of the vendor’s firmware (from Lantiq) that mattered in your case as opposed vendor’s firmware itself? Unless they patched the latest firmware from Lantiq that includes a bug fix in TP-Link’s own modem firmware to resolve the issue. It’s just speculation, of course. But either way, I have not looked into the chipset in use by the W9970 and whether it is problematic in other modems that use it.