Joking apart, y'all, is there possibly a thermal problem with the BT VDSL modems? Or can they literally only be used in the vertical position?
They CAN be used flat. It is just something that I picked up from using a Netgear '834GT. If a bit of kit has ventilation grills around the circumference (none on top or bottom) mounting vertically will improve the cooling sufficiently to diagnose a heat issue.
My problem is recent and I figured it was a heating issue (likely a duff soldered joint as not had it long enough for dust to be the culprit) as disconnecting the power from the unit would give 10-15 mins of good service.
Since standing vertically, with a gap under it, had perfect service.
Stress - the condition brought about by having to resist the temptation to beat the living daylights out of someone who richly deserves it.