LONDON • Container shipping, the backbone of the global trading system, is showing signs of fatigue as the pandemic descends into its darkest days. Carriers reaping the biggest profits in at least a decade are struggling to operate reliably as bottlenecks worsen around ports from southern England to Shanghai, contorting supply chains for everything from car parts to cosmetics to medical equipment. Just 50.1 per cent of container vessels arrived on time last month, down from 80 per cent a year earlier, and the lowest level in records dating back to 2011, according to a service reliability index compiled by Copenhagen-based Sea-Intelligence, an analysis and data provider. Delays can add costs, induce operational headaches and restrain revenue for the shippers of cargo - companies like Costco Wholesale. The Issaquah, Washington-based chain of 803 warehouse-size stores on four continents expects the situation involving container shortages and late deliveries to persist for a few more months. "There are instances of 50 per cent or 100 per cent or even more sale increases of an item, and if we could procure more, we'd have even higher sales," Mr Richard Galanti, Costco's chief financial ...