Your image and post shows what I wanted to confirm; that you are using the default Video/Movies view with a list style of Thumbnails. Sometimes people are using custom views and don't mention it.
I understand from what you have just said that not only does the thumbnail for "Hail, Caesar" not show in the Video/Movies view, leaving just the movie with the default thumbnail, but the movie itself disappears from the view. Usually if Cover Art just isn't available then MC will show the movie with the default thumbnail, like the first screenshot I have attached to this post. Then after a short time MC will grab a video frame and use that as the Cover Art, like the second screenshot I have attached. Of course it should look like the third screenshot I have attached.
The observation that the movie completely disappears from the Video/Movies view leads me to believe that the [Media Sub Type] must be getting changed when you run the "Get Movie & TV Info..." process and select TMDb, but not when you select Rotten Tomatoes. Which would be quite strange, because that isn't happening on my system. Very strange as you say the movie shows up in Theatre View with its Cover Art.
Anyway, check the [Media Type] and [Media Sub Type] tags are "Video" and "Movie" respectively, via the Video/Files view, and change them if not, then see if the movie re-appears in the Video/Movies view.