SpaceX stock slides 25% from its $225.64 peak as short sellers face billions in mechanical buying pressure from passive index flows after its June IPO.

About 40 million SpaceX shares are sold short, roughly 5% to 7% of the shares that are publicly available to trade, according to an estimate by S3 Partners.

SpaceX shares rebounded Tuesday, halting a three-day slump that saw over $600 billion vanish from its valuation. The stock climbed significantly after a brief dip below its IPO…