Four Starbucks CEOs over five years have blamed lost sales on its struggle to keep its thousands of U.S. stores reliably stocked with coffeehouse essentials like milk, pastries, and cup lids.

Current CEO Brian Niccol has made fixing the shortages a main measure of his turnaround campaign.

But shortages at Starbucks are a more deeply rooted problem than has been publicly reported. And Niccol¡¯s ongoing efforts to keep shelves stocked have so far met with limited success as he encounters outdated technology and a splintered network of suppliers, according to interviews with 10 current and former Starbucks corporate employees, including senior managers.