It's almost a meme now that Stray Kids and Red Velvet always comeback at the same time, but this coincidence even goes back to 2018!!
August 6, 2018:
SKZ "My Pace"
Red Velvet "Power Up"
December 2018:
Both groups were promoting Get Cool and RBB at the same time
June 19, 2019 aka the day the kpop world was shook by the release of the 2 iconic noisy masterpieces catered for intellectuals only:
SKZ "Side Effects"
Red Velvet "Zimzalabim"
June 2020:
SKZ "God's Menu" on June 17
Red Velvet Irene & Seulgi's sub-unit was originally scheduled to debut on June 15 but was then postponed to July. However, the two groups promoted at the same time later on
August 2021
SKZ "Thunderous" on August 23
Red Velvet "Queendom" on August 16
March 2022
SKZ "Maniac" on March 18
Red Velvet "Feel My Rhythm" on March 21
They were even nominated against each other on music shows:
and now the tradition goes on
October 2022
SKZ Maxident on October 7
Red Velvet Seulgi 28 Reasons on October 4
As a stan of both groups, this is my favorite kpop coincidence I can think of 
That's all for today and let me just drop two videos of RV (mostly Yeri) jamming to SKZ to finish off this OP
