Flow board history doesn't include the pagination that all other history pages have. At the top and bottom of the history page, there should be a line that says:
(newest | oldest) View (newer 50 | older 50) (20 | 50 | 100 | 250 | 500)
eg. https://www.mediawiki.org/w/index.php?title=Talk:Flow&action=history has ~300 entries.
It should follow the user-preference set by "rclimit" (default 50, see https://www.mediawiki.org/wiki/Manual:$wgDefaultUserOptions )
Old Trello card: https://trello.com/c/W6JdHICk/482-paginate-the-board-history-2