[2] In 2017 all members participated in KBS's The Unit: Idol Rebooting Project; however, only Anne, Gaeul and Sebin passed the audition stage.

On 7 February 2019, it was announced that member Dal was preparing for a solo debut.

On 13 July 2019, Double X Entertainment revealed that "S.I.S will be promoting as a 4-member group with Minji, Gaeul, Anne and Sebin from now on."

Double X added on, "our contract with member Jihye recently came to an end [...] Dal, on the other hand, will be taking a hiatus from her promotions due to personal reason."

It was then revealed on Dal’s personal Instagram account that she has left the company and is no longer a member of the group.