I just wanted add to this thread because I've discovered a hidden buff that was causing the solution you provide to fail where the Brave trait had been equipped even if removed.
My sim had the Brave trait equipped so I removed this. When I equipped the Fear of the Dark trait, I recieved a notification that my sim had the trait but the trait wasn't properly equipped. It wasn't showing in the Sim's traits panel under Simology and the steps to remove it weren't successful since the fear of the dark Buff kept returning.
However, I use Deaderpool's mod that enables both traits AND buffs to be removed or applied at will and I happened to notice that my Sim had a hidden buff entitled "Currently Fearless" which I am guessing was related to the Brave trait and wasn't removed when the trait was de-equipped for some reason - I used the cheat rather than the mod to de-equip the trait so others using the cheat may be having the same problem. I don't know if using the mod to de-equip the trait would have removed the hidden buff. I suspect not. Anyway, I removed the hidden buff using the mod and hey presto the Fear of Dark trait could now be properly equipped and all the steps taken to remove it were successful.
Once the fear of the dark trait had been removed following the steps provide by Unsecret Identity, I was able to re-equip the Brave trait and the fear of the dark Buff has not returned.
I hope this might help someone who's having trouble. Unfortunately, unless EA actually fix this, it seems that the issue with the glitch caused by the Brave trait can't be fixed without Deaderpool's mod or something similar that allows hidden buffs to be viewed and removed.
