Taiwanese smartphone maker HTC is set to part company with its COO, the latest in a number of high-profile departures at the company, according to Bloomberg.

Matthew Costello will step-down after less than three years at HTC, but will remain as an “executive advisor” after a move to Europe. His role will be taken on by Fred Liu, president of engineering and operations, who will be responsible for “operations, quality, sales operations and services”.

The departure comes as HTC recovers from a troubled initial rollout of its One flagship smartphone, a device that is crucial in the company’s recovery. Supply chain issues meant its launch was delayed across a number of markets, losing a head-start it could have had over Samsung’s Galaxy S4.

According to figures released by HTC today, there are some positive signs. Sales of TWD29 billion ($970 million) in May 2013 were up 48 per cent from TWD19.6 billion in April, as volumes of One ramped.

While the May sales were down 3.35 per cent year-on-year, this compares with declines of 44 per cent in February, 48.6 per cent in March, and 36.9 per cent in April.

And US number one operator Verizon Wireless said in a tweet yesterday that it is set to add One to its portfolio “later this summer” – creating an important opportunity for the vendor.

Late last month, it was reported that a number of executives had left HTC, with its marketing department hit especially hard – which was attributed to Ben Ho, its CMO, wanting to return planning and strategy control to Taiwan.

A number of product and corporate heads have also moved on.