We haven't tried the game on the EZ Flash Air, but maybe you could try the following things and see if any of them fix it:
1. Make sure there are no ADDONs (reset/cheat) enabled in the EZ Flash menu, as these will attempt to patch the game, and could break it (such patches are generally intended for games made with the Nintendo SDK, which Goodboy isn't - I do believe the EZ Flash team added support for our game at some point, but not sure how stable it is!)
2. Make sure you're on the latest firmware (Firmware 3/Kernel 1.04). https://www.ezflash.cn/download/
3. Don't unzip the ROM directly onto the SD card - this has caused issues on our own EZ Flash devices. Instead unzip the rom to your PC first and then copy it across.
If you're still having issues, please also try holding A + B + Down + Left while the game boots up, to view the ROM checksum. It should show '159FF629' - if it shows anything else then this means the ROM might have been corrupted or had patches applied.
Viewing post in Goodboy Galaxy (for GBA) comments
Want to chime in that I do get graphical glitches after a while, when playing through the EZ Flash Air. The firmware/kernel is up-to-date. Is 159FF629 still the checksum? I downloaded the latest version of Goodboy Galaxy and am getting "1b36ecf1" as checksum.
Edit: After running the checksum again, I get a different one. Something funky is going on!
Yet another edit: I've loaded the game onto NOR and manually setting the SAVE TYPE to SRAM, now I consistently get "90F6B869" as checksum. When loading the ROM into mGBA on my computer I get "159ff629". Setting the game to SRAM does seem to help, but needs some more research.