Though Chipotle has been focused on winning back all the customers it lost during its food-safety crisis, a company executive says some restaurants don’t have enough food to feed the people who do want to eat there. And those food shortages are making customers cranky.

The shortages have become an “increasingly frequent problem” as some restaurants miscalculate demand and don’t make enough food, Mark Crumpacker, Chipotle’s chief marketing officer, said on a call with analysts reported by Business Insider.

“Running out of food is a very common occurrence at Chipotle,” he explained. “It’s hard to do — to keep up with the demands in exactly the right way.”

Among the other factors that have contributed to to a less-than-satisfactory customer service experience (as recently noted by Chipotle’s newly-solo CEO, Steve Ells) complaints about food shortages have gone up recently, according to Chipotle’s internal surveys: It’s the No. 2 complaint behind long ordering lines, and just ahead of messy dining rooms, Crumpacker said.

The company says it will improve training to address the recent shortages.

“When trained properly and focused on the right things, they can do it [right] every time,” Crumpacker said.

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