I'd say 11.6 is the problem regardless of what anybody says.
Denying empirical evidence doesn't add to your credibility; if anything it makes your reply seem ignorant, not to mention utterly useless as far as troubleshooting goes. Correlation does not equal causation. I can deny the existence of buffalo all day, but them walking around sort of proves me wrong Lol.
Since I doubt you'll get my metaphor, I mean that these system updates have been reverse engineered by more than capable people. Had there been any "breaking" issues it would be widely known. All firmware changes are documented on 3DBrew so you can have a look yourself and see that 11.6 didn't change a thing that would even cause this. The last firmware update that broke ANYTHING of note was 11.4, and it didn't cause this either.
It boggles my mind that people seem to automatically jump to an assumed conclusion based on absolutely nothing. Contrary to popular belief (and I'm getting tired of saying it over and over) electronics are
bound to fail eventually. Five years is normally the max. If your system starts acting funny out of nowhere or suddenly stops working or something, chances are it's normal hardware failure. Unless you are using a NEW Nintendo 2DS, the chances of your console being manufactured in the last 2 years is slim to none. So, if anything that should be your first assumption.
As for the issue at hand, I can't offer a solution because not enough information is given. People also seem to forget that things they have done to their console (that caused an issue back then or "went away, even if it didn't cause an issue earlier it may have not been recognized properly) 100% have an effect on the way it runs now. How many times do people edit the homemenu, forget and then try to update while getting an error, blaming the console, Luma and everything under the sun except themselves; when it was entirely user error.
This happens constantly when people see, "Oh CFW, let me just install that! Hmm, something is wrong, let me mess with this and this and this and that. Damn, now I forgot what I did. Oh well, it's fixed now let me continue"
"OMG, I think I bricked my 3DS! Help! How did it get like this? I don't know, it just
suddenly stopped working but it was fine before, it must be this new firmware! No? Then it
must be this new game I installed! No, I didn't mess with my system at all! I got an issue before but I fixed it and don't remember how and now this is happening. Help!!"
EDIT: Sorry OP even though my reply is a bit of a rant there is still some good advice in there. I was a bit "triggered" by the pompous assumption. It's getting tiring with all these people offering bullshit for advice.