Shein’s march toward an initial public offering has gotten tangled in a web of regulatory scrutiny on three continents this year. Now, as its executives try to restart IPO talks, executives at the fast fashion retailer face another problem: having to explain a first-half slump in the business.The company’s revenue growth decelerated to 23% in the first half of this year, from 40% last year, two people with direct knowledge of the matter said, a result of rising competition from Chinese bargain s...