As Chipotle closes the books on its second consecutive year of bad headlines and sagging sales, the company’s founder and co-CEO Steve Ells says the burrito chain still has “a long way to go” to recover from its food-safety crisis. In particular, he notes that Chipotle has forgotten about providing the best customer service.

Chipotle had its worst stock decline in six weeks, and Ells says that’s partly because the chain has lost its focus on the customer experience, leading to slower lines at it restaurants.

“I’m not satisfied with the rate of recovery,” Ells said during an investment conference in New York reported by Bloomberg. “I’m particularly not satisfied with the quality of experience in some of our restaurants.”

Chipotle has been trying its best to lure customers back into its burrito-filled arms by launching a new loyalty rewards program, showing off new food-safety procedures, dessert, better online ordering, and giving away lots of free food.

Some of that has paid off, and trust in the brand has almost returned to where it was before the food-safety disaster, Ells said. But slow customer service could turn off customers who have come back to the chain, only to find it an imperfect experience, he added.

“2016 has been the most challenging year in our history,” Ells said. “We obviously have a long way to go.”

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