Actually, what Space linked is the cause of your issue.
Replays that are saved via "Export to validate" seemingly contain no ghost car or map file. It's just the validated data from the run. The replay can be uploaded to MX, and it works for comparing times, but there is nothing inside the replay to "watch".
Lately people have been using "export to validate" to upload their autosave replays, since MX had broken the ability to upload autosave replays.... because they were trying to prevent people from uploading StadiumCar in Canyon replays and vice-versa.
I don't know what can or should be done, but that's the state of things.
I'm really happy to see the Nadeo leaderboard up in any case.