Probably just a brainfart from me, but do you have Digital Voice. I replaced my HH hub with a Smarthub 2 to support digital voice and was surprised when my VDSL sync speeds dropped by about 10Mb when the DV service was enabled. The router then rebooted every couple of days with the speed increasing by a few Mb each time. At the time I assumed that this was a feature of DV enablement rather than standard DSL line profiling as the speed increased back to normal when the HH5 was plugged back in. In any event after a couple of weeks my Smarthub 2 had recovered to the full speed.