I checked the last round of translation notifications and out of few hundreds edits there were 4 which were not top revision:
https://meta.wikimedia.org/w/index.php?title=User_talk%3AFerdous&diff=9604870&oldid=9604186
https://meta.wikimedia.org/w/index.php?title=User_talk%3AAnn_jordan999&diff=9604872&oldid=9604190
https://meta.wikimedia.org/w/index.php?title=User%20talk:Johalmohammad&action=history
https://meta.wikimedia.org/w/index.php?title=User%20talk:M.s.fernando&action=history
They appear to be specific users who for some reason keep receiving two copies of each notification. Maybe someone can check if there's something special about them in the jobqueue logs or in the DB?
See also T73548: Duplicate message occasionally sent due to redirects not being de-duped properly