Make sure you have the newest version and so on, then use <> to change speeds, but let the replay play with normal speed at least once, only after playing once its speed can be changed. If you load via menu, it's not necessary unless you click quick load (which skips the part that automatically prepares replays for playing at different skips, hence quick).
Also if the replay is old, it's not impossible that something's not working in it; you could probably try editing it's last frame and saving it anew to see if it improves situation.