Lip syncing is not new in the kpop industry. It is not a surprise when many idols lip sync their performances. Majority use a backtrack with their voice, aka as AR and sing over their parts. You won't be able to tell they are singing live unless you are close to the stage where you can know if they are pitchy or they have haggard breathing.
Idols also pre-record their live performances and then lip sync on actual stage.
Gfriend were caught lip syncing on a live radio broadcast of Sukira for the promotion of their song "Me Gustas Tu" in 2015.
Tiffany of SNSD was lip syncing on her first week of promotion for her solo debut on the song "Once in a Lifetime" in KBS Music Bank in 2016.
Hyuna, Psy girl and ex 4minute member lip synced her KPOP Music concert MAMA stage of her hit song "Red" in 2015.
D.O. (Kyungsoo) of Exo lip synced his performance of "Open Arms" with three other members, Baekhyun, Chen and ex-memeber Luhan, in their WAPOP concert back in 2013.
Yeri of Red Velvet forgot to sing her line but her voice was still heard in their stage in 2015. It was the first time the girls performed their debut song "Happiness" after the addition of 5th memeber, Yeri.
I.O.I, the nation's pick, were caught lip syncing their first week of promotion of their song talk talk talk in M-net Mcountdowm in 2016. Sejeong seemed to forget her line.
Nayeon of the most popular k-pop girl group, Twice was caught lip syncing in their stage of hit song "Cheer Up" in WFMF Kpop Concert in 2016.
Irene of Red Velvet was also caught lip syncing when she had no mic on her but the song continued with no hitch in 2015.
Tiffany was again caught lip syncing on the title track of her solo debut, "I Just Wanna Dance" in Mnet Mcountdown in 2016.
SNSD Seohyun also lip synced her "Stranger" performance over 3 times at 2016 SBS Drama awards in 2017.
Onew, leader of Shinee, also lip synced the performance of their hit song "Lucifer" back in 2011.