There was mention on twitter of a 'technical problem' but the sources aren't reliable and I cant find anything from AF themselves. Must have been something to cause concern considering the rate of descent.
Edit: just checked again, AF are saying;"#AF454 false indication but application of precautionary principle. Safety always comes first. Passengers taken care of by AF"
So basically "woops"
https://twitter.com/AFnewsroom/statu...32180462108672