Hundreds of workers at a technology factory in China clashed with authorities and flooded past isolation barriers after weeks under lockdown, a stunning breakdown in the Communist Party’s efforts to contain Covid-19 infections. The Shanghai factory, which is owned by Taiwan’s Quanta Computer Inc. and makes devices for Apple Inc. among others, has been operating under tight restrictions since the beginning of April. In a video shared on Twitter and YouTube, workers rushed through barriers and tangled with guards in white protective gear who tried to keep them inside. Quanta employees confirmed the clash occurred Thursday evening, while the company...