At least three of Bytedance Ltd.’s major investors have marked up the TikTok-owner’s valuation to more than $400 billion, a sharp rebound for a Chinese social video leader that has been threatened with a US shutdown.SoftBank Group Corp.’s Vision Fund revalued the company to north of $400 billion in December, factoring in potential for its artificial-intelligence business Doubao, according to people familiar with the matter. Investing giants Fidelity Investments and T. Rowe Price Group Inc. have ...