The further information that you have provided is useful but inconsistent.
You need to stop being fixated on this estimated line length value that the router states when not even syncing. You can disregard it, estimates are just that and not accurate.
I tend to agree with the comments @dect has stated in his reply, in particular the fact that the copper goes back to the exchange but the VDSL signal moves over to fibre at the FTTC cabinet.
Looking at the router stats you have provided for the 80/20 service these are not the same as the previous data you gave which as I thought were for a much shorter line probably in sync at the full 80/20 which would explain the high SNRM values so I am ignoring that data.
The stats for the Cisco show the 80/20 service in sync :-
DS Channel1 DS Channel0 US Channel1 US Channel0
Speed (kbps): 0 64501 0 16315
Noise Margin: 6.1 dB 6.0 dB
Line Attenuation: 16.7 dB 0.0 dB
Line Attenuation(dB) by frequency band 11.4 28.3 44.7 5.4 23.0 36.5 N/A
That looks perfectly normal for a line around 500 metres to the cabinet, my line is around 400m and the attenuation is 15.1dB
For the 40/10 service, I have no idea why you changed to the lower speed.
I notice this is using a different Cisco modem/router
DS Channel1 DS Channel0 US Channel1 US Channel0
Speed (kbps): 0 39998 0 8496
Noise Margin: 11.2 dB 6.1 dB
Line Attenuation: 0.0 dB 0.0 dB
Line Attenuation(dB) by frequency band 11.1 28.3 46.0 5.2 23.1 36.4 N/A
Again it all looks correct, the upload is bit below the expected 10Mbps but it is different firmware to the previous stats. Broadcom based modems sometimes don't show upload attenuation, this one doesn't show anything for the combined attenuation figures but the per band values are very similar to the previous stats.
I am struggling to understand what your actual problem is. You have a working connection that could be running at 64.5Mbps download if you had stayed on the 80/20 service.
The only thing that you seem to think is a big problem is that the Digi router fails to sync and you have come to the totally incorrect conclusion that it is out of range of the DSLAM.
The router stats from the Cisco devices show that you are still connected to the same cabinet as I stated in my previous reply.
The Digi Transport WR44 router is a bit of an odd device and seems to require a lot of custom configuration to work on BT FTTC. Perhaps there is some small change on a SOGEA service that has stopped it working, I don't know what that might be and I'm 100% sure no Openreach engineer will have a clue. They will just say use another router.
Edit: I have seen your later posts are you saying the service does not work with the Cisco routers?
I have no idea what a clear counters command does or why it should drop the connection.
Edited by Realalemadrid (Fri 19-Feb-21 13:54:06)