Had it happen in the 320 (sim) the other day.
The FMGC's had dropped to independent mode for some reason.
One went left one went right, quickly changed the AP's over to the side going the correct direction and kept a good eye on it.
In the end was told to pull the cb and reset the fmgc, did the trick and sorted it out.
Don't know if this was just a sim bug or happens in the same way on the a/c.