Trying to interperate..
Assuming the runway is obscured/fouled a "CAT3B failed passive?" would as I assume downgrade you to CAT IIIa (no rollout). Meaning get you to the threshold but not maintain RWY centerline during rollout.
The other interperation is that most A/C I have dealt with are completely capable of performing a CAT3 landing on 1 A/P. Most people assume that the other channels are active but in most if not all cases they are passive, good old example is the 27, the "B" servo only monitors tolerances with the "a" servo that allways is in command. This logic is shared by many other airframes during CAT landings, only one A/P is working, the others are monotoring for disagreements.