“Titane” director Julia Ducournau made a triumphant return to Cannes Monday evening with her new feature “Alpha.” The mother-daughter infection thriller earned an enthusiastic 11.5-minute ovation after its premiere — one of the most glowing in-person receptions thus far at this year’s film festival. As the applause raged on, Ducournau grew visibly emotional, wiping tears away and making a heart with her hands as a sign of gratitude.
But the premiere of “Alpha” faced a brief interruption when, about an hour into the film’s runtime, attendees in the balcony began waving their phone flashlights. Some audience members shouted for a doctor in French, asking…