A320 A/Thrust Failure
A/Thrust fails in flight with AP1 engaged so to recover autothrust you can engage AP2 so that it runs on the FMGC 2 channel. With the APP p/b pressed on the FCU for an ILS approach, you go to press AP1 again. After looking through the FCOMS and other notes I reckon you will only get CAT3 single as AP1 will not engage.
My reasoning behind this is that AP1 is the master when you have AP2 engaged also (CAT 3 Dual) and therefore runs off FMGC 1 however the Autothrust cannot run off FMGC 1 due to the earlier failure of the A/Thrust. I have gathered an understanding of what is going on here but cannot find a definitive answer after sifting through the books.