Travis Scott says he postponed his AstroWorld concert in Buffalo Thursday night because of illness, but we're told it's more complicated than that ... because Kylie accused him of cheating and he's staying in L.A. to deal with it. Also, 21 Savage just got a big break in his deportation case ... the D.A. has rejected the felony case against him involving a concert promoter who claims he took $17,000 without performing.