To understand the challenges facing Six Flags Entertainment FUN -4.38 %decrease; red down pointing triangle, look no further than Siren’s Curse. The new roller coaster opened in late June to rave reviews at Cedar Point, its theme park on the shore of Lake Erie halfway between Cleveland and Toledo, Ohio. The problem: Siren’s Curse has broken down so many times that it’s becoming a punchline. Maybe, the joke goes, the ride is actually cursed. ...