Hey all- to answer your boiling questions regarding the 'replay' button, in efforts to improve stability of the game the devs have made some changes today and any attacks older than 21:00 UTC will not show replays for either attacker or defender. Another note we'd like to make is that the replay button will only work on attacks from players who have the same or prior versions of the game as yours. For instance, if your attacker has the most recent version of DomiNations, and you have the previous version, you will be unable to review the replay. If you and your attacker both have the same version of the game, you will be able to review the replay.
We would like to clarify that this is not a bug, but do let us know if you see any anomalies with the 'replay' button in the future. Thanks!