A quick update :
F-GZCD has not flown between 2 and 9/10 but remained in CDG, so I suppose it has nothing to do with cabin retrofit (too short + location).
F-GZCN stayed only briefly in PGF (3 days). It returned to service on Oct 5. Too short for a retrofit and it’s normally not the location to do it.
So it seems no plane is undergoing retrofit for the last 3 weeks, as the status of F-GZCC in heavy maintenance in CGK is unsure retrofit-wise. I have the feeling they are running very late on their schedule...