Do You Use Console Screenshot/Video Capture?

Because replays record inputs rather than a video of the match, it is possible for replay contents to differ from the original match when played back.

If a character or other element is loaded during a match faster than expected (such as because of pausing or online lag), then the replay of that match will "freeze" and finish loading the element before it can continue.

A common error noted in replays mostly experienced in Brawl is that they may "desync" over time; the effects vary, though among the most common are actions occurring that did not previously occur, excessive lag followed by significantly increased playback speed, and the replay abruptly ending. With the Pokémon Trainer, particularly unusual effects can occur, such as him sending out a Pokémon which never loads or leaves the revival platform. Replays of Wi-Fi matches are more likely to desync than local matches due to the frequent lag experienced in games, but local replays can also be subject to the problem. The cause of "desyncs" is unknown, though it is speculated it has to do with save data of replays becoming corrupted by some outside factor. In addition, it is possible for a replay that plays fine to randomly desynchronize when played again, and after some tries, play correctly again. Some Special Smash modifiers can also be responsible for desyncs, as some modifiers like Curry and Speed directly affect the speeds of characters and other actions.

Gameplay mods can also cause desyncs to occur, as many mods modify the characteristics of combatants, thus preventing the saved match from properly running. For similar reasons, Smash 4 warns players after they save their first replay that updates to the game can potentially cause replays from older revisions of the game to no longer function; furthermore, all updates that adjust game balance prevent the playing of older replays and provide an option to mass-delete them. Ultimate followed this example initially, but recent patches have addressed this issue by retaining old patch data, so older replays no longer desync and do not need to be deleted. This change is known to have existed since Update 6.1.0.

When uploading a replay to YouTube, there is a small chance that, at some point during the process of converting the replay into a video, the music will suddenly stop playing for a few seconds. If this happens, the game will erroneously state that the post was cancelled. Additionally, posting the video disables the ability to post screenshots on Miiverse or take screenshots using the Wii U's Image Share feature. In order to post screenshots online again, players have to restart the game.