LONDON/LOS ANGELES—Supply bottlenecks, slower product deliveries, and higher freight and labor costs risk shifting the fast fashion industry into the slow lane, as shown this week by British online fashion retailer ASOS. A business model that aims to bring new styles into stores every three or so weeks and where shoppers expect to see fresh, reasonably priced merchandise on each visit is discovering its limitations. “When it comes to fast fashion, it’s all about being first to market,” said Gus Bartholomew, CEO and co-founder of SupplyCompass, a London-based firm that specializes in product development and delivery software for fashion brands. “What we’re seeing with most brands is that they’re all still massively struggling with visibility and control around delivery certainty—knowing when things are going to be delivered and when things might be likely to go wrong and how that will actually impact them.” Shares in ASOS fell 16 percent on …