Some accounts that Facebook Inc. has said appear to be tied to Russian entities and bought ads around the U.S. election continued to post divisive messages as recently as this past August, according to saved versions of the now-deleted pages.

“Secured Borders,” a Facebook page that the social-media giant told congressional investigators bought ads during the presidential campaign last year, posted messages after the election that called for killing Muslims and that labeled illegal immigrants as “rapists, murderers, child molesters,”...