I'v had the same problem.
I was still getting errors by luma after complete installation.
SO i figured uninstall CFW cause it might causing any problems.
I was on ver. 11.6.0 now i was able to access settings (cause most of the time i get freezes)
game card isnt even working properly also i get error, while when cfw was on it it worked.
I did also a complete system format.
Somehow im stuck on 11.6.0 and my 3ds will not boot automatic configuration screen. (just light up black screens) Sometimes im able to boot trough save recovery mode. last time i did this i was unable to update.. now i'v readen something about primary and secondary dns.. i will try this.. anybody else formiliar with this or can help?
Thanks!