still been having the disconnections andi now see it does have nothing to do with maximum data rate its ny noise margin,i watched it drop at exactly 8.00 pm last night down to 0db on the downstream it stayed there for ten minutes but did not drop connection and then went back to 3.5db but it disconnected at around 1.00am this morning and this is how it goes on.
As can be seen from your latest post of the router stats your data rate shows as the maximum speed your line can support. Only thing I can suggest seeing as you say the line is quiet and the engineer found no faults is try a third party router. VDSL routers are available from many outlets, the TP-Link TD-W9970 for example can be had for about £30.
If you want guaranteed IPv6 support then be prepared to spend a bit more for Asus, Billion, DrayTek or FritzBox devices.