A Cannes police source said authorities were investigating whether a second incident of vanishing jewels was a theft, a problem of inventory or a loss, a source said.
Another Swiss jeweller, Chopard, had gems worth $1.4 million stolen in the first week of the 12-day festival on the French Riviera.
Police said the Chopard jewellery had been in the safe at Suite Novotel hotel in central Cannes, which had been rented by an employee of the jeweller.
The entire safe was removed from the wall and taken during the night of 16 May.
Someone entered without forcing the door, a police source said.
A spokesman for Chopard, a sponsor of the Cannes festival, later played down the report, saying values had been exaggerated.
Jewellers and fashion houses use the world's largest film festival at Cannes as a promotional showcase, lending gowns and accessories to celebrities who are photographed.
More top news
A group of soldiers has broken an Antarctica record by becoming the first all-female team to cross the continent using only muscle power.
Gunmen have attacked the Intercontinental Hotel in Kabul with casualties feared.
The Grammy-winning singer posted a picture of the two on his Instagram saying the two got engaged right before the new year.