It is now just a series episode, not a movie. Hence why there is no poster.
I solved that dilemma another way: with a collection.
Reasoning is that the movies are in no way connected to the series. They are more like a re-telling of parts of the series. Hence they are not required to be watched between or after a certain episode and are more loosely connected.
That’s why I think a collection is more apt.
see How to add movies in a TV library? - #4 by OttoKerner
