you aren't giving enough information. How are you loading Luma3DS, for example (using a bootloader or not)? Also, READ THE WIKI linked in the first post of the Luma3DS thread. It more than likely has the fix for your problem. Most problems I've seen people have would have been fixable by those people if they had informed themselves with the wiki.
for what i know that firm_agb in luma folder is useless at this rate or i'm wrong? exp if you are under a9lh,i install gba only in sysnand(all works perfectly)and play there leaving emunand for other things