So after giving the 8-bit Music Power cart more than a few tries, I discovered that I could get it to show the intro with the "Riki" logo for a bit, but then it inevitably crashes after a few seconds.
I found this out after slapping the cartridge against my leg a few times. Yes, seriously. And the more I slapped it, the longer the intro ran for. After a short while the cart only shows the white screen again, but a few more slaps will get it going for a bit again. But it still always eventually crashes after a few seconds. I couldn't get past the intro, except if I pressed the start button. But that only leads to it trying to load the menu and glitches out the same way every time.
The reason I started slapping the cartridge was that I know on the Amiga 500 computers you could sometimes fix RAM bootup errors by dropping the Amiga against the table from a few inches up, which could reseat the RAM chips if that was the problem. So my first theory was that maybe the chips were somehow not properly seated. But bending the PCB slightly seems to also affect it. So my theory now is that some of the traces in the PCB are broken or something, and that slapping/bending it slightly re-aligns them for a bit, but ultimately it won't work.
Still haven't heard anything from Play-Asia btw.