US - French military last week had deployment exercise with V-22's deployed from USS Kearsarge in the Red Sea, to operate on the French Mistral class
LHD Tonnerre ship in the Mediterranean.
In 2015 the French navy declared the V-22 Osprey fully qualified for operational missions to and from the Mistral class.
I suspect the aircraft are now sitting in Nice waiting for the US ship to catch up and come pick them up.