I think something is off with your characters motion vectors, and that it is likely being generated by something you are doing in your animation. We can confirm this by disabling Anti-aliasing, motion blur and any other temporal effects like Lumen temporarily.
Then, if the ghost disappears, we can be confident that the motion vectors are wrong, causing the compensation techniques used to prevent blur are not working as intended.
You can also use the motion vectors debug visualizers but they can be a bit tricky to parse. Incorrect or missing motion vectors are the primary cause of ghosting artifacts.