[edit]: we discovered this is a problem with the openFPGA core on certain batches of Analogue Pocket. (more info here) Downgrading the core to 1.0 will fix it.
Original response below:
You may have a faulty SD card - we experienced a similar problem during development, but it wasn't the game's fault.
If you want to verify the ROM, you can try holding A+B+Down+Left while booting the game. If it doesn't show 'A4A932B1' then that means the ROM is corrupted.
Also if you're using a flashcart, please make sure all add-ons/patches are disabled (use 'clean boot' on the menu)