This isnt just happening in Plex Web. It is happening in all of the clients I have tried.
I have 2 different movies. They happen to have the same name and release year. If I search for that movie, the new search results dropdown thing only shows 1 result and 1 thumbnail. Clicking on that takes you to a selection with no thumbnails and multiple options. Basically you just have to guess which movie is the one you want.
Edit: Looks like you found a bug in the search algorithm.
I’m seeing the same thing using Chaos (2005) {imdb-tt0405977} and Chaos (2005) {imdb-tt0402910}.
Workaround: Using Plex Web, edit one of the movies and change the title. For example, if I change one of the movie titles to Chaos I, both movies are listed when searching.