And it happened again, same thing, same line, this time for around 1 hour duration. What happened was that Mrs Weaver plugged in a Huawei SmartAX MT882 into line cwcc@a.1 = BBEU20700042, then about ten minutes afterwards, line cwcc@a.3 = BBEU20700055 went bonkers, cycling, going down / up / down again for about an hour and then calmed down on its own as far as I can see. The remaining line - cwcc@a.4 = BBEE20709519 - showed a burst of packet loss around the time that cwcc@a.3 went nutty, but none of the cycling behaviour.