Consider various physical effects in metals that have been discovered over the centuries, such as magnetism, conducting electricity, the thermoelectric effect (and its opposite manifestation the Peltier effect), the photovoltaic effect, hydrogen embrittlement, piezoelectricity, and superconductivity. Each of these has one mechanism, and only one mechanism, as far as I know.
It seems unlikely to me that anomalous nuclear effects in highly loaded metal hydrides are caused by many different phenomena with different physical principles. I do not think there are any other physical effects in metals which have two or more different disparate causes. In biology you sometimes find mechanisms, organs and so on that evolved independently, but came to resemble one another, such as the body shape of dolphins and fish. That's another story entirely. - Jed
