This has happened on Super Mario 3d Land, Mario Kart 7 And Monster hunter stories.
Land had the hack "Jump mid-air" active and crashes when going into a world that isn't a mystery box (I think that's what it's called)
Mario kart had "instant acceleration rev1" and "instant acceleration rev0" active. Crashes when closing game or leaving a race
Monster hunter had multiple hacks active, so I cannot pinpoint what caused the crash.
What can I do to fix this? I'm very new to 3ds hacking. Let me know if you need any more information! (The image shown is the 3d land crash)