You are not wrong

I suspect (but have no data or knowledge to support this) that there is some kind of dynamic authentication going on somewhere between leaving the BBC and arriving (or not) at my ID41. And that somehow this authentication does not survive very small network disconnects caused (possibly) by my ethernet over power plugs. That hypothesis fits the facts but I have no way of confirming it empirically.
For example, I just loaded 10 CDs into Sooloos without problem while getting interrupts on R4 - all devices connected to the same dumb switch after the power plugs except the MD600.