(Bloomberg) -- GameStop Corp. shares spiked and then quickly dropped in postmarket trading Monday after cryptic social media posts showed up and then disappeared from the social media account of Keith Gill, the financial influencer known as “Roaring Kitty,” who became prominent during the 2021 meme-stock craze. Most Read from BloombergIran Makes New Offer on Uranium in Response to US, WSJ SaysInside a Year of Chaos and Conflict at Kevin Hart’s Media CompanyTrump Rejects New Iran Peace Offer as ‘