On Keyakizaka46's official website, it was announced that member Imaizumi Yui would be halting her activities. 

Last weekend, Imaizumi took a break from work due to her poor health. After seeing a doctor, it was determined that she needs treatment and rest for a fixed period. It is uncertain when she will resume her activities, but will be announced when decided on the group's official website. 

Get well soon!

Source & Image: natalie