Hey @laoo have you tried booting Alpine Games in Felix? It has a similar behavior to Handy, where the game won't boot past the initial screen; it just fades to black and the CPU loops endlessly. I know where it is getting stuck, but am not sure why it fails on emus. I'm guessing some of the hardware sprite types are not commonly used in games, and are not being emulated properly.
If you want more details, let me know and I can provide disassembly where it's failing. Or you can disassemble too if preferred.
A related issue, beyond the scope of Felix: I can manually patch Alpine Games in the Handy debugger to make it boot properly (but of course hi-color mode does not work well). But I don't know how to re-encrypt the cart. I am guessing the code is using some kind of checksum on individual overlays, and thus it fails to execute if I patch the ROM instead of patching it live in RAM.