If you have Cat 3 DUAL in inop sys on status page then try...FCOM 4 irregularities!
If "CAT 3 DUAL" is displayed in INOP SYS without any other failure being detected :
CHANGE the AP in command. It may allow the CAT 3 DUAL function to be recovered.
If this procedure fails :
SET FAC 1 pushbutton to OFF, and back to ON
WAIT for FAC 1 fault ECAM warning to disappear, and
APPLY the same sequence for FAC 2.