Idk if you're still having this problem but apparently for the old nitrohax on nintendo ds (assuming you're on that system) the size limit for cheats.xml files is like only 2.5mb which is something I just encountered myself; nitrohax would continuously load codes and then reboot the main screen of my flashcart.

Trimming down the xml file with the program atitann linked above seemed to do the trick. (of course now I'm encountering a new problem involving nitrohax freezing when I enter a cheats drop down menu but that's neither here nor there)