You've probably run into one of the many known issues with the new start/stop/pause/resume recording feature.
I'd suggest you stop using it on whichever server/world you were on until the issues have been fixed (so at least until the next version).
You will likely find recordings which failed the start/stop/pause/resume post-processing inside the replay_recordings/raw folder. Simply moving them one folder up should make the visible in the replay viewer.
PS: Your Minecraft isn't actually visible in your video for some reason.
