Have you got an Android tablet or phone? It would be helpful to use Wifi Analyzer to make sure that you suddenly didn't get a neighbouring source which is now interfering with your signal. (Wifi analogue video senders are the worst, though thankfully nobody really uses them any more.)

I know you said it works fine on MacOS but that could still be auto-channel negotiation, with that driver picking a nice clear channel and maybe MorphOS failing to.