So on the Shield Tablet K1 and the newest Retroarch, several cores (in particular Picodrive) are completely broken and FCEumm won’t read FDS games, while NEStopia will.
Is there a fix?
FCEUmm loads FDS fine here. Maybe you’re missing a BIOS?
Other than that, yeah, broken picodrive is a known issue. Google broke it with Android 6.
It can’t be the bios because Nestopia recognizes and loads the BIOS just fine.