Rakuten Group’s shares sank the most in over a year after the Japanese e-commerce pioneer failed to slash persisting losses at its mobile unit.

The Tokyo-based company’s stock fell as much as 12% on Wednesday, their biggest intraday drop since April last year. One-time tax credits and surging fintech segment gains helped Rakuten report its first net income in six years. But investors focused on losses at the company’s mobile operations, which were little changed from a year ago.

Billionaire founder Hiroshi Mikitani led Rakuten’s commercial foray into Japan’s saturated wireless operations six years ago. Since then, the company’s grappled with stubborn losses and mounting debt. Even before Wednesday’s drop, shares have underperformed the broader market this year with a 14% decline.

That’s despite a 59% profit gain in Rakuten’s fintech segment, which includes the banking, brokerage and credit card, as well as 57% profit growth in the mainstay internet services segment with Rakuten’s travel and shopping sites. Those gains were before considering mobile ecosystem contributions.

On Monday, the company said its operating profit more than doubled in the June quarter. The performance still trailed analyst estimates. Japan’s stock market was closed for a holiday on Tuesday.

“Overall profit improvement remains on track, although mobile earnings growth was slightly weak,” Morgan Stanley MUFG Securities analysts including Tetsuro Tsusaka wrote in a note.