Installed Luma3DS and GodMode9 on the 3DS to view the system files. When turning on the 3DS (not the first one mentioned in this post, a second one that was able to access Safe Mode but still could not reach the Home Menu) with these installed I got an error message "prefetch abort (svcBreak)".
Followed the instructions [link|https://wiki.hacks.guide/wiki/3DS:Error_screens/Luma3DS_exception_screen|here] for the specific error message to fix it: "If R5 contains D900458B: The f000000b folder in SYSNAND CTRNAND is broken, its exact location being at [1:]/data/<ID0>/extdata/00048000/f000000b.
To fix, backup f000000b by pressing R+A while highlighting it, then selecting Copy to 0:/gm9/out. Once it is backed up, delete the folder. If this does not fix the issue, copy the folder back where it was."