You missed that entire discussion about the changing nature of the wall of the faithless didn't you?
The actual existence of the wall is entirely unknown at this point. It was turned into a mirror during novel events, only to get revoked by SCAG, which then had it's entry for the wall of the faithless get removed in an errata.
As far as we know, it's still a mirror, until another more recent sourcebook comes along saying otherwise.
Errata is too late for some of us; TT campaigns have already dealt with the wall. Retconning is a no-no in TT games.
This is the problem with story errata, and errata in general. I believe in 'death of the author', once it's published and bought, done. It's over. Save it for the next publication.
Unless something's causing trouble at the table, errata hasn't any business. And besides, players almost never look it up.
