As noted, Sami Zayn and Kevin Owens were both sent back to the U.S. after last night's SmackDown taping. According to Sports Illustrated, it was said that they were sent home "for conduct deemed detrimental to the WWE."
According to Pro Wrestling Sheet, Zayn and Owens didn't follow directions given to them during their segment with the New Day during last night's SmackDown taping as they were supposed to "feed" New Day after Zayn vs. Kingston. The plan was for Owens and Zayn to continue attacking New Day after the match - getting pushed back each time they tried - until finally retreating. This was meant to get a bigger reaction for New Day. Owens did jump in the ring after Kofi won the match, but Zayn and Owens quickly exited the ring afterwards, which just left New Day standing there, making for an awkward ending to the segment.
The report also said the duo has become "increasingly difficult to work with" and have been "unhappy backstage." Although involved in the Team Raw vs. Team SmackDown storyline as SmackDown roster outcasts, neither currently have a match at Survivor Series.
Source: Pro Wrestling Sheet