SISTAR's agency, Starship Entertainment has apologized for Soyu's less cheerful appearance at the group's recent appearances, including the fan signing event on Friday.

In the fan signing event, held by SISTAR for a shoe brand for the girl group, at Seoul Time Square, reporters pointed at Soyu's gloomy facial expressions. In several blogs and social media comments, Soyu was described to be not smiling and not having a good time.

Starship Entertainments has apologized and explain the issue.  According to the agency, Soyu is still recovering from a back injury sustained from the "Kyung Joo Hallyu Dream Concert" on Sept. 20. The SISTAR member is also suffering from the flu, AllKpop reported.

"Soyu's condition wasn't good after she hurt her back at a concert. She's receiving treatment and completing her schedule, but her condition even worsened as she's suffering from the flu. We apologize that she wasn't able to show a good image to her fans at the fan signing today. We plan to minimize her schedule from now on," said Starship.

Soyu's poker face has been captured at the M! Countdown on Oct. 1, fan signing on Oct. 18, and Music Bank on Oct. 9.

The idol has been joining SISTAR's activity while also promoting in individual projects, like one she is set to collaborate on with her brother Su.

Soyu's fans have called out Starship for overworking her.