well, now we know FLAP 3 isn't the same a config 3. What if we have config 3 and both channels failed at exactly this position. Still an auto land?
If both flaps channels or both slats channels fail, you lose AP 1 & AP 2.
In my opinion, having your flaps locked at
exactly Config 3 or Full seems quite remote.
If it would happen, refering to 3.02.27 p1 (talks about less than config 3) and 4.05.70 p16 (talks about abnormal config), you can autoland if really needed, if your flaps are not at an abnormal config (So only at exactly Config 3 or Full)
Personally, I would only do it if there is absolutely no other option.